VACCINATION

Vaccination. THE Encyclopædia contains no separate article on the subject of Vaccination; but Small-pox, in the article MEDICINE (224), is concluded, with a notice of its introduction. We now propose to give a condensed view of the subject, and of the present state of medical opinion on the merits of Vaccination.

On the 14th of May 1796, Edward Jenner, a physician in Berkeley, near Gloucester, first applied to the arm of a healthy boy of eight years, by means of two superficial incisions, the morbid fluid secreted by a sore on the hand of a dairy-maid, who had contracted Cow-pox from the udders of her master's cows. The seventh day after the operation he had uneasiness in the arm-pit; on the ninth, became chill, had headache, lost appetite, was otherwise indisposed, and spent a restless night; but the following day, was free from complaint. Of the appearances of the local sore, we have no particular information, but that it resembled a bluish pustule, was surrounded by an erysipelatus or red circle, and afterwards formed scabs and eschars without producing other inconvenience. The object of this operation, which was chiefly experimental, was to ascertain the degree of immunity from small-pox contagion thus obtained; and on the 1st of July, therefore, variolous matter was inserted by inoculation, but without being attended with the usual disease; and when this was repeated some months after, the same effect was observed. Further inquiry was prevented, in consequence of the disease disappearing till the spring of 1798, when it once more made its appearance among the dairies of Gloucestershire. On the 16th of March, a child of five and a half years was inoculated with matter taken from the teat of an infected cow. On the 6th day after the operation, he was unwell, and vomited; but on the 8th appeared to be in his usual health. The progress of the local vesicle was similar to that of the former case, except in the absence of the livid or bluish tint observed. On the 28th of March, the disease was transferred from the arm of this patient to that of William Pead, a boy of eight, with the usual appearances, and especially the red circle, quite similar to that which is observed after variolous inoculation. To this redness Dr Jenner first applied the term areola. From the fluid produced in this case, several patients, both young and adult, were infected, and in all, the phenomena appear to have been pretty uniform; or, at least, with deviations so trifling, that they do not require particular notice. From the previous conclusions derived from persons who had been affected with cow-pox, and who resisted the variolous action, it might be presumed to be unnecessary to try how far those who had been artificially subjected to cow-pox could resist small-pox. To render his conclusions more certain, however, Dr Jenner tried it without effect on his first vaccinated patient; and with the second and last cases, his nephew was equally unsuccessful.

Such were the first trials of the effect of vaccine fluid on the human subject; and so far as they were carried by Dr Jenner, the results appeared to warrant the main conclusion, that the process of vaccination renders the human body unsusceptible of being acted on by the infection of small-pox. We must not omit to remark, however, that the Inquiry of Dr Jenner shows that he had formed, in the year 1798, no very distinct idea of the nature and phenomena of the vaccine disease, or, at most, that he imagined it to be identical with small-pox. It is evident, that, in his early researches, Dr Jenner believed that the origin of small-pox could be traced to the heel of the horse; and that though cow-pox was a disease transmitted from the horse, and modified by the system of the cow, it was specially identical with, or allied to variola, and differed in variety only. On this principle, he applied to it the denomination of variola vaccine; and it is obvious that he was confirmed in this opinion by observing, that a person who had suffered the vaccine disease is not liable to be affected with small-pox contagion.

The singular facts announced in the Inquiry, and their more extraordinary application, recommended by Dr Jenner, attracted much attention; and shortly after its publication, Dr Pearson of St George's Hospital commenced an investigation, in which he collected many facts tending to render its history more complete, and to demonstrate its power in enabling the human body to resist the contagion of small-pox. In one point only did he disagree with Dr Jenner,—the origin of the cow-pox from the heel of the horse; in denying which, he was supported by the arguments of Dr Parr, and the experiments of Mr Simmons of Manchester.

Dr Pearson's examination of this subject was followed at no long time with Further Observations by Dr Jenner, the chief purpose of which was to confirm the conclusions delivered in the Inquiry, and to establish the leading fact, that vaccination renders the human system unsusceptible of small-pox. As some cases had come to light of this disease occurring in the persons of those who had undergone the vaccine disease, Dr Jenner, by ascribing these to a spurious form of cow-pox, conceived he had removed any exception to the truth or general accuracy of his doctrine. Of the spurious form, he conceived there were four sources: The 1st, From pustules on the nipples or udder of the cow, without specific virus. 2d, From matter, which, though originally specific, had undergone decomposition. 3d, From an ulcer proceeding from the genuine disease, but at an advanced stage. 4th, From matter generated by the human skin, after contact with peculiar morbid matter, formed in the system of a horse. These various positions Dr Jenner illustrated or proved by arguments, either direct or analogical, derived chiefly from similar phenomena, exhibited in the progress of variolous poison. Of these arguments, the most import-

Vaccinations. ant are those which relate to differences or variations induced in the genuine poison by elementary decomposition, or by the process of ulceration, after the period of the proper lymph was passed. The propriety of admitting the 4th cause as a source of imperfect vaccination is intimately connected with the origin assigned to cow-pox by Dr Jenner; for if a modifying effect on equine matter be assigned to the udder, it is impossible to suppose that the former can have a genuine influence on the human constitution, or on the small-pox.

The interest excited by the singular facts disclosed in Dr Jenner's writings, with the confirmation which they derived from Dr Pearson's inquiry, quickly gave rise to the wish of bringing the truth of the doctrines thus advanced to the test of experiment; and men were eager to ascertain what practical advantage was likely to result from the introduction of cow-pox artificially excited, and the substitution of a mild disease, derived from a brute animal, for a human malady, which, even in the most favourable circumstances, was liable to be attended with much danger. The merit of this practical application was reserved for Dr Woodville, who, in January 1799, introduced into the Small-pox Hospital of which he had the charge, vaccine matter derived from the milk-cows in Gray's Inn Lane. On the 21st January 1799, Dr Woodville applied, by a single puncture, to the arms of seven persons, matter in a purulent state, obtained from the teats of a cow labouring under the disease; and on the 24th he infected three persons with vaccine matter taken from the sores of Sarah Rice, a young woman who had contracted the disease in the course of milking. From these two sources, this physician affected 600 persons, of various ages, with the vaccine disease; of whom the circumstances of 200 are recorded in the Reports of his practice. In most of these patients, inoculation of small-pox matter was performed at various periods after the application of the vaccine disease, with a view to ascertain the genuine power of the latter, and to discover what influence it could exercise in deranging or modifying the progress of the various disease. The general result of these experimental cases may be given in the following terms: 1st, In about three-fifths of the whole number, the operation was followed, at intervals of various length, by an eruption of pustules, more or less numerous, over the cutaneous surface. (P. 151.) In one case, in which these pustular eruptions appeared about the seventh day, and was attended with convulsive motions, death took place on the eleventh day after insertion of matter. (P. 149.) 2d, In persons on whom vaccine matter and variolous matter are inserted at different arms, but at the same time, the local affections resulting from each application preserved their characteristic appearances through the whole course of the disease. (P. 139.) 3d, When the two fluids (variolous and vaccine) are rubbed together, and inserted by a lancet dipped into the mixture, sometimes the vaccine pock, sometimes a variolous pustule, has been produced, the

respective characteristics being in either case retained Vaccinations throughout; and in some rare instances, both diseases are thus produced. (P. 104.) 4th, If inoculation be performed alternately with variolous and with vaccine matter every day till fever take place, both inoculations make progress; and as soon as the whole system is disordered, they appear to be all equally advanced in maturation. (P. 145.)

It cannot now be doubted, that, though the experiments of Dr Woodville have thrown much light on the nature of the vaccine disease, and on its true influence over the poison of Small-pox, yet they were conducted without due regard to the legitimate mode of ascertaining the truth. 1st, The patients on whom Dr Woodville operated were exposed to the atmosphere of a small-pox hospital, where, of all other places, the air was most likely to be thoroughly impregnated with variolous effluvia. 2d, In the greater number of the patients vaccinated by this physician, inoculation with variolous matter was performed at a period a great deal too early to ascertain the counteracting force of the vaccine disease. 3d, It is doubtful whether, in his selection of vaccine matter, he chose the proper period; for he informs us that the matter was taken from the animal in a purulent state, which we now know is very unfavourable to the success of the vaccinating process. (Jenner, p. 113.) 4th, Dr Woodville formed a very erroneous notion of the nature and distinctive characters of the vaccine and variolous diseases; not only in considering, like Dr Jenner, "the vaccine variola, and the human variola, to be only varieties of the same disease, rather than distinct species" (p. 152, 153); but in the further error of supposing Cow-pox capable of exciting a general affection of the skin. Our more perfect knowledge of Cow-pox has shown, that its action on the skin is confined to those spots only to which it is applied, and that it never hitherto has been known to produce general eruptions similar to itself. This error is intimately connected with another committed by Dr Woodville, in believing cow-pox capable of communication by effluvia, or by any other manner than that of absolute contact.*

The results of Dr Woodville's experiments, so different from those obtained by Dr Jenner, were communicated to this gentleman at first apparently in a private manner (p. 129); and, in order to submit the matter to a fair trial, London vaccine fluid was transmitted to Dr Jenner, who inoculated several persons, (twenty,—eighteen at the manufactory, two previously, p. 133), without any other difference of effect than a greater degree of local inflammation, and with an eruption of a few red spots, which quickly disappeared without maturing.

It was in a subsequent publication, however, that Dr Jenner undertook the task of examining the experiments of Dr Woodville, and showing the circumstances from which the different results proceeded. The anomalous appearances he here ascribed to the action of variolous matter which had crept into the constitution with the vaccine; 1st, Because a great

* Jenner, p. 86. Further Observations. Pearson, p. 50, Proposition VI.

Vaccination. number of the persons vaccinated by Dr Woodville were inoculated on the 3d or 5th day with various matter; 2d, Because, in the Gloucestershire dairies, where cow-pox had been known time out of mind, no pustular eruptions had ever been known to appear on the general cutaneous surface; and 3d, Because, though the proportion of pustular cases was at first 3 out of 5, they afterwards diminished so much, that of the last 100 persons inoculated, only seven had pustular eruptions.

To bring this matter to a more satisfactory determination, Dr Jenner procured fluid from an affected cow belonging to a farmer in Kentish Town, and transmitted it to Dr Marshall, who was then extensively engaged in vaccination in Gloucestershire. Under his care 423 persons had undergone, in the course of some weeks, the process of vaccination; and of this number it appears that 127 were infected with the matter sent by Dr Jenner from London; yet Dr Marshall positively states, that neither in the first set of cases, nor in those thus vaccinated, had any pustular eruption occurred, or been observed. (P. 158, 159.) In one case only did a pustule appear in the elbow of the inoculated arm, and it matured. The same result was obtained in the vaccinations conducted by Dr Jenner personally, and in those by his relation, Mr Henry Jenner. (P. 162.) From these facts, therefore, Dr Jenner concluded, that the vaccine matter obtained from an animal reared in the neighbourhood of London was not different, at least in its effects, from that which was obtained from animals affected with the disease in Gloucestershire. It is proper to notice, however, that Dr Jenner acknowledged that some of his correspondents had mentioned the appearance of eruptions at the commencement of their vaccinating operations; but "in these cases," he remarks, "the matter was derived from the original stock at the small-pox Hospital."

Another point in this inquiry, viz. the immunity from subsequent small-pox afforded by vaccination, came under the investigation of Dr Jenner at this period. Although the evidence upon this point had been already conclusive, yet, as various facts were constantly coming to the knowledge of Dr Jenner to prove the protecting power of vaccination, and its influence in counteracting small-pox, even when the system is under various action, he published several of these proofs, in order to show the true power of the vaccine disease. These cases are in every respect similar to many others which have since occurred, and it is unnecessary to bestow further notice on them. Shortly after, a second Tract appeared from Dr Woodville; and though his object was to refute the assertion of Dr Jenner regarding the adulteration of the vaccine matter of the Small-pox Hospital in London, his testimony was of the utmost advantage to the anti-variolous power of vaccination. It will be remembered, that, towards the conclusion of Dr Woodville's vaccinations, the varioloid or pustular eruptions which had been so frequent at the beginning, began gradually to diminish, and finally almost to disappear; and in the further prosecution of this physician's experimental investigation, we find that these eruptions were found al-

most never to succeed the process of vaccination. Vaccination. In his Observations on the Cow-pox, which appeared in July 1800, many important facts were disclosed, which tended directly to unfold the true properties of the vaccine disease, and the relation which subsists between its action and that of small-pox. It is unnecessary, at this distance of time, to enter into the merits of the charge which Dr Woodville conceived Dr Jenner brought against the vaccine matter of the Small-pox Hospital, and of the mode in which Dr Woodville attempted to repel it; and as we do not conceive it tended, in the slightest degree, to illustrate the question, of the cause of the pustular appearances after vaccination in that Hospital, it may be passed over in silence. The more important and not less interesting subjects of Dr Woodville's pamphlet were the fact of the disappearance of these pustular eruptions, and the circumstances under which they disappeared. 1. The vaccine matter of the Small-pox Hospital, after which pustular eruptions had so generally appeared, was employed in two situations in the country, in vaccinating more than 1000 persons, in two of whom only did any pustules, resembling those of small-pox, appear. 2. Though Dr Woodville denied adulteration of the vaccine matter with matter of small-pox, he was, however, obliged to admit, that the cases of vaccination in the Hospital "had been, and still continued to be, influenced by some adventitious cause, independent of cow-pox." This was proved by the results of vaccination practised in the hospital by matter obtained from many different animals: by the results of vaccination practised on persons at their own houses, in various districts of London, by Dr Woodville and other medical gentlemen who employed the matter from the same stock; and more decidedly by the result of vaccination practised on three patients at Hospital, with matter obtained from the same cow, from which Dr Jenner took the matter employed in the vaccinations of Dr Marshall. In one of these patients no fewer than 100 varioloid pustules appeared; and other instances, equally conclusive, appear to have taken place. 3. Among many children residing in various parts of London, to whom Dr Woodville transferred the disease, through the medium of the Hospital matter, no instance of matured pustules had occurred during the twelve months succeeding to the introduction of the practice. 4. The pustular eruptions which had been so common after vaccination, at the early period of the practice, became much less frequent. Of 310 cases of vaccination, after the publication of the first Reports, 39 were attended with pustular eruptions in the following order:—In the first 100, 19; in the second 100, 13; and in the last 110, only 7; and at a later period they appeared in the proportion of 3 or 4 only in the 100.

From these various facts, Dr Woodville very justly drew the inference, that the cases vaccinated at the hospital differed from those vaccinated elsewhere, in being placed in the centre of a variolated atmosphere, to the operation of which the pustular eruptions were to be ascribed. In forming this conclusion, however, he committed the singular paralogism of supposing that the cow-pox excited these pustules, or was, in

Vaccination—other words, the direct cause of the varioloid disease; and he, therefore, imagined that the variolated atmosphere of the Hospital, the existence of which he willingly admitted, was only a co-operating cause. It is obvious that this extraordinary doctrine owed its birth to the previous opinion which, we have already remarked, he formed of the nature of the vaccine disease,—that it was not confined to the spot to which lymph is applied, but was capable of extending its action over the whole cutaneous surface. Had Dr Woodville not allowed himself to be misled by this erroneous principle, there is a strong presumption, from the language in which he expresses himself, that he would have arrived at the true conclusion which recent and accurate observation have at length succeeded in establishing.

When the facts above noticed are considered, we conceive it will not be difficult for our readers, if they keep in mind the points originally ascertained by Dr Jenner, respecting the local action of the vaccine disease, and the necessity of its being communicated by application of its proper fluid, to comprehend, that the pustular eruptions over the cutaneous surface of the vaccinated were not excited, as Dr Woodville concluded, by cow-pox, nor arose, as Dr Jenner suspected, from mixture of various matter with vaccine, but were the immediate results of the variolous atmosphere in which the individuals were placed. The different degree in which they appeared in the early and more recent period of Dr Woodville's vaccinations, will form no valid objection to this conclusion, when it is remembered, that the frequency of pustular eruptions in the first vaccinations, depended on the abundance of variolous effluvia necessarily existing in a small-pox Hospital, or the saturation of its air with this matter;—while their subsequent rarity was the effect of its gradual diminution by the division or diminution of its cause, and of its final extinction by the substitution of another disease. That admixture of variolous matter had not taken place, there is every reason to conclude; as we know, from the experiments of Dr Woodville, that it is impossible to produce in this manner a mixed or neutral disease, but that each preserves its distinctive and appropriate characters. The post-vaccine pustular eruptions should have suggested another conclusion,—that the vaccine disease does not entirely extinguish the variolous, or prevent its appearance, but renders it milder, less tedious, and, to a certainty, destroys the chance of its fatality. That this conclusion escaped Dr Woodville is by no means wonderful, especially when it is remembered, that the general belief of the profession was, that a second attack of small-pox was an occurrence so rare, as to be considered next to impossible. "Happy is it for mankind," says Dr Jenner, "that the appearance of the small-pox a second time on the same person beyond a trivial extent, is so extremely rare, that it is looked upon as a phenomenon. Indeed, since the publication of Dr Heberden's paper on the Varicella or chicken-pox, the idea of such an occurrence, in deference to authority so truly respectable, has been generally relinquished." It is worthy of

remark, also, that Dr Woodville not only admitted this Vaccination inference in its fullest extent, but applied it, in the same unlimited construction, to the immunity afforded by vaccination against the variolous disease. "This circumstance, then," says he, (that is, the immunity afforded by cow-pox), "appears to be as much a general law of the system, as that a person having had the small-pox, is thereby rendered unsusceptible of receiving the disease a second time." (Reports, 155.) On this subject it is only necessary to remark, that Dr Thomson of Edinburgh has shown, in the most convincing manner, that the non-recurrence of small-pox has been admitted on far too slender grounds; and that the writings of physicians contain sufficient evidence, that small-pox may occur at least twice, if not three times, in the person of the same individual. Had this important proposition been known, or admitted to its just extent, at the period when vaccination was introduced, there is reason to believe, that the appearance of pustules on the persons of those who had been vaccinated, would not have occasioned so much perplexity to the friends of the practice, or triumph to its enemies, and that its true merit would have been more justly, and not less quickly appreciated.

During the progress of Dr Woodville's experimental inquiries, the merits of vaccination began to be understood, and the practice had been coming into general and extensive use, both in London and in the more remote counties of England. The publication of Dr Woodville's second Tract may be regarded as marking the epoch of its general admission, and announcing the adoption of it in Public Charities, and in the practice of the most eminent surgeons. The united efforts of Drs Pearson, Lettsom, MM. Moore, Ring, &c. and other philanthropic or professional individuals, contributed powerfully to its general introduction; and though opposition was at first shown, the more candid and intelligent part of the profession at length admitted the advantages of vaccination over artificial variolation. It is unnecessary to bestow any notice on the objections which were urged by writers of a certain class, and which, as they were founded on prejudice have now sunk into a well merited oblivion. The efficacy of vaccination, as an anti-variolous agent, was, indeed, so generally admitted, and the practice was so widely introduced, that its benefits were extended, in the course of a few months, to many thousand persons, in different towns of the kingdom; and were conveyed by different channels to Paris, to Vienna, to most of our colonies, and to the United States of America. In the meantime, the impression created at first by the appearance of pustules in the vaccinations of Pearson, Woodville, Ring, Dunning, Goldson, and others, seemed to have worn off completely, or to have been forgotten; and the great bulk both of the profession and of the public considered the occurrence of small-pox eruptions, after vaccination, either impossible or so rare as to be regarded as a physiological anomaly. The general credence of this maxim did not arise from the complete absence of pustular eruptions after vaccination, as we shall see, but evidently depended on the idea of the distinctive nature of chicken-pox, or the inaccurate notions of small-pox itself then prevalent; and also on the great

Vaccination. expectations formed of the powers of the vaccine disease in counteracting or extinguishing the poison of small-pox.

The truth of these assertions is abundantly confirmed by the subsequent history of vaccination, and of small-pox eruptions occurring either sporadically or epidemically in various parts of the country. We have already seen, that Dr Jenner was led to infer the absolute immunity from small-pox conferred by the process of vaccination, and to consider the vaccine disease so similar to small-pox, that when the human body had undergone the former, it was no longer liable to attacks of the latter. This doctrine was admitted by many professional persons in terms much more unlimited, if possible, than those in which it had been understood, even by its first promulgator. Dr Jenner was, indeed, inclined to qualify it in some degree; but the professed partizans of vaccination, from a well-meant idea, perhaps, that it would weaken public confidence, and render the adoption of vaccination less easy than was consistent with public safety, opposed every approach to such an opinion, and defended strenuously the anti-variolous properties of the vaccine disease.

It is scarcely necessary to mention here, that, since the time of Dr Heberden, a vesicular, or vesiculopustular disease, not unlike small-pox in its local appearances and constitutional symptoms, had been distinguished from it as a separate affection under the name of Chicken-pox. Almost all the instances of pustular or small-pox-like eruptions which were observed after vaccination, were referred to the head of chicken-pox; or if they were not sufficiently similar to this disease, to be referred to it, they were admitted to be small-pox, but occurring only in persons on whom vaccination had been imperfect in action, or improperly performed. In other instances, the appearances of the eruption were so fallacious, or the ideas of the observers so little precise, that of those who saw them some contended that they were chicken-pox, and others small-pox.

Although cases were not unfrequent in which practitioners of experience and knowledge were obliged to admit the occurrence of small-pox, in the persons of those who had undergone vaccination, Dr Willan appears to have been the first who had courage and patience sufficient to examine the matter coolly, and to show the exact weight of evidence by which it was supported. In the fourth section of his interesting treatise on Vaccine Inoculation, this physician has collected several cases which occurred to himself, or within his own personal observation, and referred to those collected by authors since the introduction of the practice of vaccination. As many of these were thought by several physicians and surgeons to have been chicken-pox, and as this indicated want of precision in the characteristics of the disease, Dr Willan, in his seventh section, gave an account of those marks by which he conceived chicken-pox in three different forms could be recognised. And it is by no means unimportant to observe, that the distinctions which Dr Willan established among the various forms of cutaneous inflammation, and the precision with which he expected the eruptive diseases to observe those characters, prevented him from tak-

ing those general and more just views of post-vaccine small-pox in which physicians have since coincided. Little change, therefore, appears to have taken place in the opinions of professional men, farther than to admit the occurrence of chicken-pox, and of a modified small-pox after vaccination; or, if the appearances were too strong for this construction, to consider the vaccination as imperfect and ineffectual. Such, in general, was the tenor of the Reports of the Vaccine Institutions, of our various public charities, and in some instances of scientific Colleges; and so unani-
Vaccination.
mous and decided was the language of those bodies, that individuals were unable to form their own opinions on objects of daily observation, or were prevented from expressing them by the fear of being regarded as either incapable of observing, or unable to communicate the genuine and perfect form of the vaccine disease; or, in short, as enemies to a practice, the pious object of which was to counteract a foul and fatal disease, and to increase the probable chances of human life.

The publication of these Reports did not, however, cause the complete extinction of post-vaccine small-pox, or prevent the appearance of the disease; and cases continued to occur even after the process of vaccination was admitted to be satisfactory, and in the observations of physicians, whose knowledge and experience gave no ground for doubting the fact. It cannot be expected, that all these cases have been published, or that their full extent can now be ascertained; for it is easy to see, that they would be often disregarded, and sometimes studiously concealed. To understand, however, the merits of vaccination, and its influence in controlling small-pox, sporadic or epidemic, it is indispensably necessary, for the unbiased inquirer, to be aware of the evidence which may be obtained from the cases of variolous or varioloid eruptions in the persons of the vaccinated already recorded. It was to Dr Thomson of Edinburgh that was reserved the merit of ascertaining the true powers of vaccination, and of placing in a just point of view the benefits conferred on mankind by the introduction of the practice. The cases of pustular eruption, in the persons of the vaccinated, were scattered in various works, their evidence was neglected and overlooked, and the inferences which they tended to establish were not understood, or they were disregarded. It was only by comparison with those afforded by subsequent observation, that real advantage could be derived from them. An opportunity for this investigation occurred in 1816, when small-pox began to appear in one or two points of the country, and eventually spread over a considerable extent. Had the appearance of small-pox been confined to one or two towns or villages, it is not unlikely that they might have been viewed in the same indifferent light in which they had been since 1800, and that they would have continued to give rise to the same doubts, and similar imperfect explanations, which they had previously done. Appearing, however, as they did in many different points of the Island, successively or simultaneously, and, as was afterwards learnt, in several countries of Europe, the public mind became alarmed, professional curiosity was

Vaccination awakened, and physicians resumed the task of investigating a disease which, it had been fondly but prematurely hoped, vaccination would render practically unknown. In the year 1816, accounts of small-pox,—occurring in persons of all kinds, those exposed to contagion and those not exposed,—the vaccinated, the unvaccinated, the imperfectly vaccinated,—and even in those who had previously undergone the disease, began to be transmitted to the various periodical publications; and during the four subsequent years, the epidemic continued to appear or subside at intervals, and to furnish matter for the observation and reasoning of physicians, whether vaccinators or inoculators. In Edinburgh, and various parts of Scotland, they prevailed to a very considerable extent, attended with a mortality of 1 in 4 to the unvaccinated and unvaccinated, and affecting the vaccinated in the rate of 1 to 2 nearly. Though the individual cases have been observed and collected by many different professional gentlemen, it is to Dr Thomson almost entirely that we owe the thorough investigation which the subject has at length undergone, and from whose researches have been derived the certain and satisfactory results which we now possess. This physician, equally distinguished by acuteness of reasoning, sound judgment, and habits of accurate observation, examined personally the whole of the cases almost that occurred in Edinburgh and its vicinity; and where the distance rendered personal examination inconvenient, procured, from intelligent correspondents, correct accounts of the phenomena. It was in a letter addressed to the Editor of the Medical and Surgical Journal in September 1818, that Dr Thomson first expressed his opinion of the incorrectness of the prevalent doctrines on the effects of the vaccine disease, and of the common doctrines on small-pox, chicken-pox, and modified small-pox, with which these opinions were intimately connected.

In consequence of the publication of this letter, and a subsequent one containing a series of queries tending to illustrate or ascertain the doubtful points of the subject, a great body of evidence was in a short time collected, and in various forms laid before the profession. The results, with those of Dr Thomson's very extended observation of the disease, may be found in the two works which he has recently published; and in which he has canvassed, with the greatest judgment, and in the most liberal manner, all the problematical and assumed points of the subject.

The circumstances, however, which merit particular attention, in this recent epidemic, are the strong confirmation of the truth of many of the earliest observations since the introduction of vaccination; and especially of those views which we have already shown, the experimental inquiry of Dr Woodville, if properly understood, would have suggested. The varioloid disease, at least in Edinburgh and its vicinity, and so far as can be discovered, throughout Scotland, occurred in three classes of persons; those who had undergone neither small-pox nor cow-pox, those who passed through small-pox, and those who had undergone, in a satisfactory manner, the process of vaccination.

In these several classes of patients, it was found Vaccination. that the different forms of varioloid eruptions described as pure small-pox, modified small-pox, and chicken-pox, co-existed during the epidemic, and were capable of producing each other. It was observed, for example, that individuals who, after vaccination, presented eruptions, termed modified small-pox or chicken-pox, were capable of communicating to those who had neither undergone vaccination, nor had been affected with small-pox, an eruptive disease which could not be distinguished by competent judges from small-pox. (Thomson, Varioloid Disease, p. 45, and p. 207.) It was also found, that the same contagion or the same infecting source, produced cases of coherent or confluent small-pox in the unprotected; and cases of chicken-pox, or modified small-pox in the vaccinated, or even in persons who had many years before passed through small-pox. The obvious conclusion from these facts is, that if small-pox and its modifications, and chicken-pox be admitted to derive their origin from a contagious source, that contagion must be one and the same for all; and that whatever opinion be formed as to the nosological differences of small-pox and chicken-pox, as pustular or vesicular eruptions, it must be granted, that they spring from the same generating cause; and that the variations in appearance depend on something totally unconnected with the contagious agent which causes their formation. There is no means of accounting for this relation of diseases, Dr Thomson has justly remarked, unless in supposing two contagious causes, specifically distinct, existing at the same time, and in the same place, and producing their respective effects on the persons of those exposed. But, independent of the general improbability of this doctrine, it might be easily shown, that of two such distinct contagious causes as we have supposed, not only would one or other have produced its characteristic effects on a much greater proportion of the community; but these effects could not possibly have been so frequently interchanged, or so uniformly have appeared in place of each other, as the experience of the recent epidemic has shown. To render this point, which is liable to be misunderstood, especially by our general readers, more obvious and intelligible, let it be supposed, as was done after the time of the elder Heberden, that chicken-pox arose from one morbid cause, and small-pox from another, utterly different; and let it also be admitted, that both contagions are occasionally found to appear in a community epidemically; then it must follow, that the disease which depends on chicken-pox contagion ought at all times, and in all cases, to preserve distinctive characters, and that small-pox should likewise preserve the same unvarying peculiarity of appearance. No approach of characteristic features, much less complete interchange, ought to take place; and the phenomena of chicken-pox ought to be as distinct from those of small-pox, as they are from those of plague, of itch, or of leprosy. These results, however, which unquestionably flow directly from the admission which we have made of distinct contagious agents, were completely contradicted by every thing observed in the variolous epidemic of 1817.

Vaccination. 18, and the subsequent years; and it is impossible to resist or deny the conclusion, that small-pox, chicken-pox, and modified small-pox, owe their birth to the same source, are children of the same parent, and members of the same family.

It may be expected, since we adopt the conclusions to which the modesty and good sense of Dr Thomson induce him to apply the name of hypothesis only, that we ought to prove, by direct arguments, the nosological error committed by Dr Heberden, in separating chicken-pox as a distinct genus from small-pox. To this we reply, that it is not by direct arguments that the point can be proved; for, without subjecting to strict scrutiny the characters on which Dr Heberden assigned a separate place to chicken-pox, it is now agreed that the minute distinctions of Dr Willan completely failed in establishing a satisfactory difference in the generating causes of chicken-pox and small-pox. Had Dr Willan indeed given a due degree of weight to the fact which he states in the very outset of his 7th section, that he had seen since 1800 no fewer than 74 cases of varicella, which were by many persons deemed small-pox after vaccination, and the remarkable counterpart of this fact, that the eruptions described in his 4th section were at first regarded as chicken-pox by several physicians and surgeons, he must have been convinced of the impossibility of establishing a difference between these diseases on no other ground than that of their vesicular or pustular character. We adhere in this case to the acknowledged maxim in philosophical inquiry, to admit no more causes than are adequate to account for the effect; and while we allow the excellence of the distinctions introduced by Dr Willan as mere terms for characteristic appearances, we deny the inference that has been drawn, that these are adequate to establish a nosological difference. It is, indeed, with those who contend for the specific or generic difference of small-pox and chicken-pox, that the task of proving this rests; and it is incumbent on them to bring forward more substantial proofs and arguments than those on which the distinction has been admitted, and which are undoubtedly inconclusive.

Though the hypothesis to which we have here adverted, evidently does not require to be supported by different arguments derived from other quarters, yet it is equally due to the merit of Dr Thomson, and to that of other physicians, whose observations have led them to similar researches, to remark, that the identical origin of small-pox and chicken-pox is an opinion at length adopted by others, both in this country and on the Continent. Our limits prevent us from entering largely or particularly into this division of our subject; but we must not leave it, without adverting to the opinions expressed by MM. Berard and De Lavit of Montpellier, and Dr Hodenpyl of Rotterdam. Small-pox prevailed epidemically in the former city in 1816, and in the latter, and various parts of Holland, in 1817 and 1818; and in both situations, not only were chicken-pox at the same time extensively prevalent, but the phenomena of both diseases were found to be frequently and generally interchanged; and they were, in other respects, so similar to those observed in Edinburgh

and various parts of Scotland, that the conclusions Vaccination. which we have above noticed were irresistible. It is interesting to observe, not only as a confirmation of the accuracy of Dr Thomson's views, but as an example of different observers, unconsciously and unknown to each other, forming the same conclusions from similar researches, that MM. Berard and De Lavit were led to announce, in 1818, at Montpellier, an opinion which Dr Thomson first published in September 1818, at Edinburgh; and that Dr Hodenpyl of Rotterdam, in the course of the same year, was led to express his opinion, that chicken-pox was the primitive form of small-pox, and could be shown to originate from the same parent stock.

The view which the hypothesis of Dr Thomson enables us to take of varioloid and varicellous eruptions, and of the relation in which they stand to the vaccine disease, suggests a more satisfactory explanation of the phenomena which these eruptions present, and of the sequences, as we may name them, which they observe, than either denying the anti-variolous efficacy of vaccination, or supposing it imperfect, or improperly performed; or, indeed, than any other explanation hitherto adopted by physicians. It has been a prevalent error with medical observers to attach a degree of mathematical precision to the phenomena of eruptive diseases, and especially to those of the several forms of variolous or varicellous eruptions; and to imagine that their appearance and effects in the human body were regulated by laws of the utmost precision. The mixture of truth and of error exhibited in this doctrine is the reason of its admission without question, and its propagation without resistance. For while it is certain that extended observation proves that small-pox may affect the same individual more frequently than once, and that its first occurrence by no means secures the individual from a second attack, it is undeniable that the maxim is so far correct in general terms, that the disease is rarely known to appear twice with the very same characters, or with the same severity in the same individual. While, therefore, the first appearance of the disease does effect some change in the susceptibility of the frame to a second attack, it is obvious that this change is neither so marked nor so uniform, nor so absolute as the opinions of physicians had hitherto represented it to be. (Thomson's Varioloid Epidemic, p. 201.) It is precisely this error which has given rise to mistakes so general on the anti-variolous power of vaccination. It was the same mode of thinking that led the more zealous partizans of vaccination to expect a form of action more absolute and determinate, and an immunity more complete than the laws of organic motions ever sanctioned. It may be urged, indeed, that to predicate what the laws of organic motions are, or what they sanction, is a mere petitio principii, a sort of assumed principle, unless we adduce facts or arguments to prove what we advance; but is it to be doubted, that the actions of living bodies, and the influence exercised on living objects by exterior agents, are not regulated by laws mathematically exact? Has the most sedulous observer ever been able to trace or to demonstrate that certainty of action, or regularity of effect, which is exem-

Vaccination. plified in matter endowed with properties merely physical? Has attentive observation of the phenomena of living bodies, and, above all, of those of the human frame, not shown, that the results of every process are influenced by numerous circumstances, and modified by causes too complicated to allow their operation to be appreciated? Such, we may now conclude, has it been with the practical application of the vaccine disease, and such will it be with every measure which is adopted in medicine, with too little regard to the character of those objects on which the physician has to operate.

It must now be obvious, that vaccination is not the positive and exact action, which it was thought to be at the moment of its introduction; and, that it does not effect on the human body that absolute change which it was originally represented to do. That it does effect a change of some kind must be inferred, not only from the phenomena of those forms of small-pox which occur in the persons of the vaccinated, but also, in a more conspicuous and forcible manner, from the phenomena of vaccination performed a second time on the same individual. The vesicle produced in Mr Bryce's test-vaccination, or even any vesicle thus produced at a period subsequent to the first one is evidently a modified cow-pox (vaccinella), and bears the same relation to the first cow-pox, that modified small-pox or chicken-pox bear to the first attack of small-pox.* But the occurrence of this vaccinella vesicle must be regarded as a direct proof that the change is not absolute, but limited; and the occurrence of pustular eruptions, whether variolous or varicellous, in the vaccinated, must be admitted in evidence to establish the same conclusion. It may, indeed, be regarded as the genuine result of extensive observation, conducted in the most accurate manner, that the process of vaccination is not exempted from those uncertainties which have long formed the impediments to exact principles and positive rules in medicine; and that it does not render the human body universally or absolutely unsusceptible of subsequent attacks of small-pox in various degrees of severity.

Nor will the results to which we have cursorily adverted, admit of more easy explanation by the objection which has so often been sought in the interruption or imperfection of the process of vaccination. It is not to be denied that vaccination has been sometimes rendered imperfect by one or other of the ordinary causes, and that it is reasonable to think that persons thus vaccinated are more likely to be subsequently affected with small-pox than those in whom the vaccine process has been regular and complete; but no proof has been afforded that post-vaccine small-pox was confined to those in whom vaccination was imperfect; and in innumerable instances in which small-pox succeeded vaccination, the latter process was ascertained to be as perfect as in those who were not subsequently the subjects of varioloid eruptions. Had there been any force in the circum-

stance, it was reasonably to be expected that the degree of modification should be in the inverse ratio of the perfection of the vaccine process, and in the direct ratio of the interval between the period of vaccination and the appearance of varioloid disease. No result of this kind has been observed either in the Edinburgh epidemic, or in those described by Mr Cross and MM. Berard and De Lavit, or that of Holland, as described by Hodenpyl; nor has it appeared, that those affected with modified small-pox had been vaccinated with fluid taken at an improper time, or had cutaneous eruptions, or other disturbing causes, to a greater extent than those in whom varioloid eruptions never took place.

The experience of the recent epidemic has amply confirmed the conclusion, that vaccination, though quite regular, and performed in the most satisfactory manner, does not preclude a subsequent attack of small-pox, in one or other of its forms, and does not furnish a positive immunity any more than natural small-pox, or artificial variolation. And it is satisfactory to think that this inference has been substantially admitted by the unbiased declaration of the Board of the National Vaccine Establishment.

But while we are obliged to qualify the doctrines of the original vaccinators with these limitations, it cannot fail to be gratifying, not only to the lovers of truth, but also to the sincere and temperate friends of vaccination, to find that the great practical results are not materially affected; and to know that our experience has shown the benefits of the practice in as strong a point of view as its most sanguine advocates could wish. Though the process of vaccination does not positively prevent a subsequent attack of small-pox, it has been incontestably proved, that it not only mitigates the severity of such future attacks, but diminishes the chance of their fatality almost to a fraction, or an infinitely small quantity. The clearest method of showing the truth of this proposition is, by contrasting the mortality of cases of secondary small-pox, that is, occurring either after the natural or artificial disease, with the mortality of cases of small-pox occurring after vaccination. According to the observations of Dr Thomson, the proportion of deaths in secondary small-pox, if two infections be admitted, is 1 in 25, and if one infecting source be admitted, 1 in 75 only (Varioloid Epidemic, p. 202); but death has taken place in small-pox after vaccination in one only of above 330 cases, which is between $\backslash frac\{1\}\{3\}$ and $\backslash frac\{2\}\{3\}$, or, in exact terms, $\backslash frac\{2\}\{3\}$ less frequently than it occurs in iterated small-pox. If to this statement be added the allowance that must be made for the numbers of the vaccinated who were not at all affected with subsequent varioloid eruptions, the rate of post-vaccine eruptions terminating fatally will be reduced to an infinitely small quantity. In the varioloid epidemic described by Mr Cross, at Norwich, of 10,000 vaccinated persons, 329 $\backslash frac\{1\}\{2\}$ were affected with

* See Dr Thomson's remarks at the conclusion of Dr Stoker's Letter in No. 77 of Edin. Med. and Surg. Journal.

Vaccination. various eruptions, of whom only one case appears to have terminated fatally. The coincidence of this proportion with that given by Dr Thomson induces us to place the greatest confidence in its accuracy; and we feel certain, that if observations be made on future cases, even this proportion will diminish. At present, in estimating the decided superiority of vaccination, in diminishing the chance both of danger and of death from small-pox, two elements must be kept in mind:—1st, That all the vaccinated are not affected with small-pox or varioloid eruptions, and even the proportion of these appears to be smaller than in instances of inoculation, or any other method except natural small-pox;—and, 2dly, That of those so affected, not above one case in 330 terminates unfavourably. These results establish, in the most convincing manner, the powers of the vaccine disease as an antidote to the ravages of small-pox; and cannot fail to prove, to the satisfaction of its most sceptical opponents, that the strong and plausible objections to which the recent epidemic was at first calculated to give rise, have been of no other use than to place the merits of vaccination in a clearer and more forcible point of view.

It is in its power of diminishing the mortality of small-pox, therefore, that the superiority of vaccination consists; and it is on this strong ground only, that its partisans and true friends should defend its general adoption. Let the governors of charitable institutions, the guardians of the poor, the parents of families, and the public at large, be convinced of the facts which we have now stated, and the inferences derived from them, and it cannot be doubted that the practice of vaccination, instead of being opposed, or apprehended as a source of new and disastrous maladies, or ridiculed as a useless and inefficient ceremony, will be dispassionately estimated, and raised to that rank among the benefits of science, to which its happy effects unquestionably entitle it. It is surely superfluous to show the duty incumbent on all ranks to extend vaccination as widely as possible, if for no other reason than to preserve the lives of their relatives during the prevalence of epidemic small-pox,—and to say that, in proportion as vaccination is general, the infection of small-pox must be gradually limited and confined, until it is almost entirely expelled from the habitations of men. There cannot be a doubt, that every variolous epidemic, especially in large cities, is developed much more readily in consequence of the practice of variolous inoculation, or suffering children to be exposed to the infection of natural small-pox; and it is equally certain, that where vaccination is general, the introduction of variolous infection is either difficult, or when introduced, it is disarmed of its gigantic strength.

Two points connected with this subject have

given rise to so much speculation, that we must not Vaccination. omit to notice them, however briefly. The introduction of vaccination, and its effects in diminishing the mortality of small-pox, have been naturally supposed by many writers to have a great influence on population, and to increase the numbers of the living at different periods of life. Some have gone so far as to imagine, that in this respect it would operate to an injurious extent, and increase the population of most countries beyond the limits of subsistence; while others have conceived, that an increase of different diseases would be necessarily occasioned by the extirpation of small-pox; and that this would be one of the great means employed by Providence, to keep the rate of population in due proportion to the means of procuring food.

There cannot be a doubt that one of the most salutary effects of the practice of vaccination is to diminish very much the mortality occasioned by small-pox, and consequently to augment, in a considerable degree, the numbers of the community in which it is practised. To understand distinctly, however, in what manner this diminution is operated, it is requisite to show the effect which unresisted small-pox exercises on the population of a community, and for this purpose we employ a familiar example derived from estimates formed in this country. In the year 1795, when the population of Great Britain and Ireland was estimated, according to the returns, at 14,724,000, it was calculated that the numbers annually destroyed by small-pox, according to one estimate, amounted to 34,260, and according to another, to 36,000. If we state it in round numbers at 35,000 as a medium, this mortality amounts to the enormous proportion of 1 in every 420; or, in other words, small-pox destroys annually 1-420th part of the whole population of the country. As it is obvious, that the population can be increased by the number of births only, as it is diminished by the number of deaths, it follows, that to obtain a just notion of the effect of small-pox in diminishing the population, we must deduct this 1-420th part from the numbers which are annually added by births. According to the most correct observations and calculations, it appears, that at the period which we have selected, the proportion of births to the whole population of the country was as 1 to 30, or for every 30 persons in the whole nation, only one is annually added by births. (Malthus, Book II. chap. 9, and Additions.) It therefore follows, that as the proportion destroyed by small-pox must be taken out of this annual addition to the numbers of the country, the fraction of $\backslash frac\{1\}\{420\}$ or $\backslash frac\{1\}\{4\}$ annually, will represent the exact rate at which small-pox retards the increasing numbers of a country, or acts as a positive check on population. It is to be remarked, that the elements on which these calculations are

* Mr Cross nowhere gives this proportion exactly; but it is correctly deduced from the average of his data in the following manner:—Dr Yellowly, from inquiries similar to those of Mr Cross, estimates the vaccinated in Norwich at $\backslash frac\{1\}\{2\}$ of the whole population, or 10,000; and of 603 persons under the personal observation of Mr Cross, 200 had small-pox, 91 had been vaccinated, 2 of whom had modified small-pox, and 1 chicken-pox; the remaining 312, who had small-pox formerly, had no subsequent eruption during the epidemic; consequently, we have the following proportional numbers, 91 : 3 : 10,000 : 329 $\backslash frac\{1\}\{2\}$.

Vaccination. founded, are derived from that period at which it is generally admitted that small-pox inoculation was most favourably conducted, and at which the smallest number of deaths is supposed to have taken place from small-pox, since it first began to prevail as a destructive epidemic among the habitations of men.

We have given this familiar, and we trust quite intelligible view of the influence of small-pox on population, because we fear, if we had attempted to follow the circuitous, but very beautiful and accurate train of analytic calculation, by which Du Villard has investigated the subject, we should have added much to the length of this article, without interesting our general readers, or affording information universally intelligible. This author, who has investigated the matter in the soundest manner, and with the most profound applications of modern analysis, has given formulae and tables for almost every possible question which the inquiry can suggest. He appears, on the principles which he has adopted, to have made the destructive or depopulating power of small-pox greater even than we have shown it to be. He gives the following results of his analytic investigations, as applied to the population of France. According to the law of mortality, in the natural state, the

Both sexes and all ages.

Now, in the natural state, 85,685 children, add to the population of 28,763,194, only 337,404 individuals, and by immunity from small-pox, they furnish farther 3,492,583, which raises the population to the number of 32,255,776. If such be the influence of vaccination, in increasing the numbers of mankind, it might appear, a conclusion sufficiently natural to imagine, that the population of many nations would increase so rapidly, as to exceed the means of subsistence, and overcrowd the space allotted for occupation. In point of fact, however, notwithstanding the operation of this cause, for at least twenty years, in several countries of Europe and America, the result has not been realized; and, though the nations of Europe were perhaps never so populous as at the present moment, this evidently depends on other causes than that which prevents the mortality of small-pox.

It is a fact which has been said to be ascertained by many respectable observers, that while the destruction occasioned by small-pox has been much di-

minished, other diseases, equally fatal, have been found to be more prevalent. We will not question the correctness of this observation, or deny it absolutely, but we must have it established on more certain and unquestionable facts and documents before it be admitted. But whether this be the case or not, it is not difficult to see that vaccination cannot possibly render the human race immortal; that children, and adults also, must die of other diseases besides small-pox; and that, as the numbers of a young community are increased by being snatched from one disease, a greater number must be preserved to become a prey to others.

We by no means, however, countenance the opinion that the mortality of other diseases will increase exactly in the ratio in which that of small-pox has been diminished; nor do we believe that this mortality is a necessary result of vaccination. It is found, on the best authority, that a perceptible diminution of mortality in children under ten years has taken place in every situation in which vaccination has been general; and it must therefore be concluded, that the number of individuals living at that age is augmented. It is obvious, however, that, unless we lose sight of the most fixed principles in the theory of population, this will have but a trifling effect in increasing the numbers of mankind, when it is remembered that it is ready to be counteracted by the positive checks to which we already alluded, but especially by the preventive check on which the number of marriages and of births depends.

(See various papers in the 6th, 7th, 8th, 13th, 14th, 15th, 16th, 17th, and 18th Vols. of the Edinburgh Medical and Surgical Journal; several articles in the London Medical and Physical Journal; Observations on Small-pox, &c. by Dr Monro, Edinburgh, 1818; Account of the Varioloid Epidemic which has lately prevailed in Edinburgh, and other parts of Scotland, &c. by Dr Thomson, Lond. 1820; Historical Sketch of the Opinions entertained by Medical men respecting the varieties and secondary occurrence of Small-pox, by Dr Thomson, Lond. 1822; A History of the Variolous Epidemic which occurred in Norwich, 1819, and destroyed 500 individuals, &c. by Mr Cross, Lond. 1820; Essai sur les Anomalies de la Variole et de la Varicelle, par MM. Berard et De Lavit, Montpellier, 1818; Select Dissertations on several Subjects in Medical Science, by Sir Gilbert Blane, Dissert. 10th, p. 334; History of Vaccination, by Mr Moore, Lond. 1817; Correspondence of the Dublin Cow-pox Institution, published in 1818; Observations on the Varioloid Disease, by Dr Stoker, Dublin, 1821.) (v. v. v.)

VAN DIEMAN'S LAND. See the Article AUSTRALASIA, in this Supplement. It appears, from a Statement of the Receipt and Income raised in this colony, and of the Disbursement thereof, for the last seven years, printed, by Order of the House of Commons, in June 1823, that the former was L.23,915, and the latter L.20,055.