(from vacca, a cow), is the artificial production of a disease, originally obtained from the cow (cow-pox), by bringing the matter of that disease in contact with the living human body.

To Dr Edward Jenner we are indebted for the discovery of vaccination. His attention was first directed to the subject by the popular belief which existed in Gloucestershire, where he resided, that those who were infected with matter from the sores on the udder of the cow, were ever after secured from the contagion of small-pox. It was not, however, till the 14th of May 1796, that he made it the subject of direct experiment, by taking matter from the sore on the hand of a dairymaid who had contracted cow-pox from the udders of her master's cows, and applying it, by means of two superficial incisions, to the arm of a boy. Pustules somewhat similar to those of small-pox, but darker in their hue, and filled with a limpid fluid, were produced, and became surrounded with an erysipelas-like red circle, but the whole died away, leaving on the inoculated part scabs and subsequent eschars, without producing any other inconvenience. On the seventh day after the operation, the boy complained of some uneasiness in the arm-pit; on the ninth he became chilly, had headache, loss of appetite, and was otherwise indisposed, and passed a restless night, but was well by next day. As the object of the experiment was to ascertain whether the cow-pox gave immunity from the small-pox, he was on the 1st of July inoculated with small-pox matter, but no disease was produced; and the same result was obtained when this was repeated some months afterwards. Numerous experiments of the same kind were afterwards made; and they ended in establishing the fact that the matter of cow-pox protected the human body from being acted on by the infection of small-pox, while it was itself a mild and safe disease, exciting little more constitutional disturbance than what resulted from the local sore.

Dr Jenner accounted for this singular fact, by asserting that cow-pox was nothing else than small-pox modified, or deprived of all its noxious qualities, by having passed through the system of the cow; and that the disease in the heel of the horse, called grease, which he showed was capable of producing the vaccine vesicle in the cow, was also but a variety of the same disease. In fact, he at first regarded both small-pox and cow-pox as originally derived from the horse.

The publication of such an interesting fact did not fail to excite general attention; and accordingly, the very same year in which Dr Jenner's Inquiry made its appearance, Dr Pearson published the results of his investigations, which tended to confirm the opinion advanced by Dr Jenner as to the anti-variolous powers of the cow-pox. In two points alone did he dissent. He regarded cow-pox and small-pox as two very different diseases, and denied that the cow-pox could be produced by the matter of the diseased heel of the horse; and he was supported in his opinion by the inquiries of Sir Isaac Pennington, the arguments of Dr Parr, and the experiments of Dr Woodville and of Mr Simmons.

Other experimentalists were, however, much more successful in confirming the opinion of Dr Jenner as to the analogy or rather identity of the disease of the horse's heel and the cow-pox. Mr Tanner succeeded in communicating the cow-pox to the cow, by inserting on the udder some liquid matter taken from the diseased heel of the horse; and the experiments of Mr Lupton and Dr John Loy corroborated the same fact. Dr Loy, indeed, found that even the equine matter produced in man as perfect vaccine vesicles as that derived from the cow itself, and afforded equal protection from the infection of small-pox. These conclusions have been confirmed by subsequent experimentalists both in this country and on the continent, so that it is now to be regarded as an established fact, that grease and cow-pox are the same complaint, modified by the constitution of the animals in which they occur.

Dr Woodville of the London Small-Pox Hospital lent his aid to ascertain, by direct experiment on a large scale, whether the introduction of the mild disease, cow-pox, was worthy of the encomiums bestowed upon it by Dr Jenner and Dr Pearson, and whether it really guarded the system from a subsequent attack of that loathsome and fatal disease, the small-pox. The results of these experiments were published in 1799, by which time he had vaccinated six hundred individuals. In most of these cases, small-pox inoculation had been performed at a subsequent period, to test the efficacy of the protective power of the cow-pox, but not one of them took the small-pox. An anomalous occurrence, however, showed itself in nearly three-fifths of the patients vaccinated at the Small-Pox Hospital. Pustular eruptions, more or less numerous, resembling those of small-pox, appeared on various parts of the body, in some cases maturing much in the same way as the pustules do in that disease, in others fading away without proceeding to the formation of matter. Dr Jenner, at the time when the circumstance occurred, endeavoured to explain it, by supposing that it was owing to some peculiarity in the air which these patients breathed, or to a contamination of the original cow-pox matter with small-pox. That it could not be owing to contamination with small-pox matter, Dr Woodville showed from the fact, that the same matter, when employed for the vaccination of individuals out of the Small-Pox Hospital, did not produce these same pustular eruptions; and some of the identical matter sent to the country, and used in vaccinating one thousand individuals, only produced pustular eruptions in two cases. Dr Woodville, therefore, very justly drew the inference, that the cases vaccinated at the Small-Pox Hospital differed from those vaccinated elsewhere, in being placed in the centre of a variolated atmosphere, to the action of which the pustular eruption was to be ascribed; a statement which was in a manner proved at the time by the fact, that though at first nearly three-fifths of all the cases vaccinated showed pustular eruptions, yet the eruptions afterwards diminished so much, that of the last hundred cases which he published in his first Reports, only seven were thus affected. Subsequent observation has shown that this was in reality the true explanation of the fact.

Dr Woodville considered small-pox and cow-pox as very closely allied in their nature, indeed, "to a very principal point essentially the same," and consequently recommended the general adoption of cow-pox, as an effectual preservative from the infection of small-pox, as perfectly safe and free from danger, and incapable of being propagated by infectious effluvia. This last he considered a very strong circumstance in its favour, since small-pox, even in its mildest form, as produced by inoculation, tended greatly It was during the progress of Dr Woodville's experiments at the Small-Pox Hospital that the merits of vaccination began to be appreciated, and the practice of it generally introduced into all parts of this country; and the publication of his observations in 1800 may be regarded as marking this epoch. At this period, indeed, the efficacy of vaccination as an anti-variolous agent was so generally admitted, and the practice so universally adopted, that, in the course of a few months, its benefits were extended to many thousand persons in all parts of this island, and matter found its way to France, Italy, Germany, Holland, Turkey, most of our colonies, and the United States of North America. Numerous were the publications, in all languages, announcing the success of the practice; and almost every one agreed in this, that it gave as perfect protection from the infection of small-pox as if the individual had once had the natural or inoculated disease.

Many of the partizans of vaccination, however, went much farther than this, and asserted that those who had once gone through the vaccine disease, were at no subsequent period of their lives liable to take small-pox. When, therefore, cases of small-pox did occur after vaccination, they endeavoured to explain away the fact, by asserting that it was not true small-pox, or that the individual had not gone through the true, but a spurious vaccine disease. This was, indeed, claiming for vaccination a power which was not possessed by any other disease. There is a class of diseases which usually occur but once during the course of life, but though a second attack is not a common occurrence, still it is every now and then met with; and there are very few medical men of any standing in their profession who have not met with cases of second attacks of measles, scarlet fever, small-pox, typhus, &c. Dr Thomson of Edinburgh, in his work on the Varioloid Epidemic of 1818, was the first to point out this clearly with regard to small-pox; and had the circumstance been duly attended to when vaccination was first introduced, it would have prevented much of the controversy which has since arisen. It was unreasonable to expect from vaccination a protective power greater than that afforded by small-pox itself; and yet it was from the advocates of vaccination advancing this doctrine—a doctrine apparently borne out by the perfect immunity afforded to so many thousands vaccinated in all parts of Europe on its first introduction—that others, who had seen cases of small-pox after it, were led to deny altogether its anti-variolous power, or at least to affirm that it only gave immunity from the disease for a very limited number of years.

It was not, however, till the year 1818, that the true value of the protective powers of vaccination was properly understood. During the years 1816–17–18, small-pox raged epidemically in various parts of Europe, and attacked both the vaccinated and variolated, as well as those who had neither had cow-pox nor small-pox. Chicken-pox was at the same time extremely prevalent, and the phenomena of the two diseases were found to be frequently and generally interchanged. Dr Hodenpyl of Rotterdam, Dr Thomson of Edinburgh, and MM. Berard and De Lavit of Montpellier, who all described this epidemic, agreed in regarding small-pox and chicken-pox as the same disease, which could be shown to originate from the same source. But the most important fact, and the one most interesting to humanity, was the ascertaining the comparative mortality of small-pox, when it attacked these three classes:—1st, the vaccinated; 2d, the variolated, i.e., those who had small-pox; and, 3d, those who had neither been vaccinated nor had small-pox. The conclusions at which these different writers arrived were nearly the same. Of those who had neither had cow-pox nor small-pox, 1 out of every 4 who were seized with the disease died; of those who had small-pox naturally, or by inoculation, 1 out of every 25 to 1 in 75 died; while of those who had been vaccinated, and were afterwards seized with small-pox, not more than 1 in 350 cases died; thus showing the great superiority of vaccination even to the small-pox itself, in protecting the system from the fatal effects of a second attack. Nor is it difficult to understand how this should happen. Small-pox is a disease not only very fatal, as proved by its cutting off a fourth of all whom it attacks, but it disfigures or renders infirm from an eighth to a tenth of those who recover. Its action is besides found to develop any latent disease, but particularly any scrofulous tendency which may exist in the constitution, and is thus indirectly the cause of death to a much larger portion of the human race than what at first sight appears. It is not, therefore, to be wondered at that small-pox, attacking for the second time a constitution thus enfeebled, should cause a much greater proportion of deaths than takes place when it occurs after vaccination; for no fact is more firmly established than this, that vaccination neither develops any latent malady, nor engenders a predisposition to any particular disease.

The fact above mentioned, of the comparative mortality of the three classes,—viz., the vaccinated, the variolated, and the non-vaccinated, has been, since 1818, repeatedly demonstrated. One of the most accurate and interesting details, and one which ought to set the point for ever at rest, is that given by M. Bousquet in his Traité de la Vaccination, as having occurred at Marseille during the epidemic small-pox of 1825. The population of Marseille, amounting to 40,000, might be divided into three classes, of which the respective numbers stood thus: 30,000 vaccinated; 8000 neither vaccinated nor variolated; and 2000 variolated—that is, who had the small-pox either naturally or by inoculation. Of the 30,000 vaccinated, about 2000 were seized with the prevalent small-pox epidemic, of which number 20 died, or 1 for every 100 affected. Of the 2000 variolated, 20 were attacked, and 4 died, or 1 in every 5 cases. Of the 8000 non-vaccinated, 4000 were affected, and of this number 1000 died, or 1 out of every 4 cases. From this it follows, that one-half of the non-vaccinated, 1–15th of the vaccinated, and only 1–100th of the variolated took the disease. But such was the difference in the comparative severity of the attack in the vaccinated and variolated, that while the variolated part of the population were cut off in the proportion of 1 out of every 500, the vaccinated part of the population only lost 1 out of every 1500; or, in other words, of an equal number of variolated and vaccinated cases, 3 variolated died from the second attack, for every one who died of the disease after vaccination.

Many similar instances might be quoted, all of them demonstrating the very great security to the individual, and the saving of life to the community, afforded by the introduction of vaccination. This is a subject, indeed, which has engaged the attention of political economists; and as it has been calculated that in Britain alone, before the introduction of vaccination, no fewer than 30,000 were annually cut off by small-pox, equivalent to 95,000 with the present population, while in France the deaths from that cause amounted to 85,685, and proportionally large numbers occurred in other parts of Europe and America, the saving of life effected by this invaluable discovery must be immense.

Though the benefits of vaccination were thus clearly proved, the public confidence in it has been attempted to be shaken by raising the outcry that the vaccine virus, if it really possesses anti-variolous powers, loses them as life advances; so that, at the end of a few years, those vaccinated individuals are as liable to an attack of small-pox as if they had never been affected by the disease. It is fortunately an easy matter to trace such an opinion to its true sources—namely, to a disbelief in the fact that small-pox can occur twice in the same individual, and to a disbelief in the identity of small-pox and cow-pox. Those holding such opinions as these see everything through the mist of prejudice, and represent every instance of the occurrence of small-pox after vaccination as an additional proof of the correctness of their theory, shutting their eyes to the facts daily happening around them, that a second attack of small-pox is not only by no means a very rare occurrence, but that it is a much more dangerous and fatal disease than small-pox after vaccination, cutting off at least three times as many victims.

As the first of these objections has, it is conceived, been satisfactorily shown to rest on no solid grounds, we are next to examine whether the second stands on any better foundation.

Every writer who has opposed vaccination, whatever may have been his other grounds of objection, has constantly set out with the proposition, that there are certain diseases which occur but once in the course of life, and which effect some unknown change on the constitution, rendering it unsusceptible of a second attack of the same disease. As they regard small-pox and cow-pox as two distinct diseases, they cannot imagine how the one disease should guard the human frame from the ravages of the other; and an eminent physician, whose powerful writings, in his younger days, did much to uphold such a theory, and to spread doubts among the people generally as to the efficacy of vaccination, but who lived to become one of vaccination's most able defendants, the late Dr G. Gregory of the Small-Pox Hospital, London, declared that "vaccination is not small-pox, but just the reverse—the antagonist principle." In order to answer such an objection, all that is requisite is to show that small-pox and cow-pox are really identical, the latter only modified by having passed through the system of the cow, as originally advanced by Dr Jenner, the father of vaccination.

It was announced so early as 1802, by Professor Viborg of Copenhagen, that at Berlin small-pox was communicated to the cow by inoculation; but the details of these experiments do not appear to have reached this country, and all attempts to repeat them have failed. It was not till 1830 that any detailed account of successful experiments of this kind were published, when Dr Sonderland of Barmen announced that he could produce the true vaccine disease in the cow at pleasure, by covering the animal with the blankets from the bed of a patient who had died of small-pox, and by hanging them up around it, that it might breathe the effluvia arising from them. In a few days, he says, the animal became sick, and pustules appeared on the udder and other parts, precisely similar to the cow-pox vesicles, and filled, like them, with lymph. This lymph, transferred to the human subject, he found to produce the genuine vaccine vesicle, together with the usual constitutional disturbance, and to protect the individual from the small-pox virus or contagion. In fact, such a change was effected on the small-pox matter, during its transit through the system of the cow, that it was converted from a virulent and fatal into a mild and safe disease.

The announcement of this curious experiment incited others to repeat it, though without success; and it was not till 1839 that Mr Robert Ceely, surgeon to the Buckinghamshire Infirmary, succeeded in proving the identity of the two diseases, by communicating small-pox by inoculation to the cow, and finding it produce the true cow-pox disease. He, however, failed to communicate small-pox to the cow after the manner found successful by Dr Sonderland. Mr Ceely inoculated heifers with the matter of small-pox, and found it to produce genuine vaccine vesicles, which ran their course like the natural or inoculated cow-pox, and furnished limpid lymph for vaccination. The lymph was employed in vaccinating many children, and differed in no respects from that obtained from the natural cow-pox vesicle of the cow. It ran the same course when introduced by punctures on the arm; did not give rise to any eruption on the skin, any more than primary vaccine lymph; and afforded equal protection against small-pox, as found by exposing the children to the small-pox effluvia, and also by inoculating them with small-pox virus; in fact, it did not in any respect differ from ordinary vaccine lymph, as obtained from the natural vaccine vesicle. Mr Badcock of Brighton established the same facts; and from 1840 up to the present day, has been able to keep up a fresh stock of vaccine lymph from cows artificially infected by him.

Nothing could be more satisfactory than the results of such experiments, for they proved, beyond the possibility of a doubt, that small-pox and cow-pox are but varieties of the same disease. It is, therefore, no longer to be regarded as an anomaly, that cow-pox should protect the system from an attack of small-pox, but it is in beautiful accordance with what has been generally admitted to be a law in nature, that certain diseases, once undergone, generally protect the system from a subsequent attack.

The chief objections to vaccination having been, it is hoped, answered satisfactorily, it only remains to show that the protective powers of vaccination do not wear out of the system as life advances, any more than those of small-pox itself. This is a most important inquiry, as nothing is more likely to prove hurtful to the cause of vaccination, and render the public careless of securing to themselves its benefits, than the belief that they would require to submit to revaccination every ten or fifteen years, and that at no period of their lives they could with certainty reckon on escaping the small-pox.

The old, and now exploded theory, that cow-pox was not small-pox, but its antagonistic principle, led to the conclusion that its protective powers wore out of the system after a certain number of years; and this seemed to be so far borne out by the fact, that occasional cases occurred where small-pox attacked in after-life a person who had been vaccinated during childhood. Several governments acting on this belief, but having perfect confidence in the antivariolous power of cow-pox, began about thirty years ago to revaccinate all the men in their standing armies, and the effect has certainly been nearly quite to banish small-pox from among them. Knowing, however, as we do now, that cow-pox and small-pox are in reality the same diseases, the former being merely deprived of all its virulence by having previously passed through the constitution of the cow, the results of these revaccinations proves extremely interesting, inasmuch as they not only afford a most unlooked for confirmation of the identity of the two viruses, but also the still more startling fact, that the protective power of small-pox itself wears out of the system, in a certain proportion of cases, as life advances, in nearly the same exact proportion as that of cow-pox itself. Thus, in all these armies, a certain proportion of the men were found to have been previously vaccinated, while no inconsiderable proportion had passed through the natural small-pox and escaped with their lives. Now, if we take the susceptibility of the constitution to revaccination as a kind of test by which we may conclude that the person who could be re-vaccinated (either after cow-pox or after small-pox) might have been seized with small-pox were he exposed to its contagion, then we have these revaccinations proving the fact that, after a certain number of years, the same proportion of those who have once previously had the natural small-pox become susceptible to a second attack as those who have been vaccinated; so that once having passed through all the dangers of the natural unmodified disease, the person, at the end of twenty-five years for instance, had no better security against a second attack than the person who had been protected by the mild cow-pox. Thus, in the Würtemberg army, it was found, on revaccinating the whole men, that in every 100 vaccinated after small-pox, 32 succeeded, 26 were modified, and 42 failed; but in every 100 vaccinated after cow-pox, 34 succeeded, 25 were modified, and 41 failed. By this test, then, whatever protection small-pox gave against a recurrence of that disease, cow-pox also gave, but with this immense superiority, that the cow-pox did not endanger life, did not engender scrofulous disease, did not disfigure the countenance, nor cause deafness and blindness, nor cut off 1 in every 4 to 8 afflicted by it, with all of which small-pox is chargeable. It would, however, be false reasoning to assume that all who are susceptible of being revaccinated would be liable to take small-pox naturally; and the small proportion of such cases which do occur, whether after vaccination or after natural small-pox, do not invalidate the general law, that a person who has once been properly vaccinated, or has once escaped with his life from the natural small-pox, in general remains protected against a subsequent attack. It is a known and well established fact, that certain individuals, who have had the natural small-pox in infancy or youth, may again be seized with the same disease in after-life, and that such second attacks are always much more dangerous to life than small-pox after vaccination. Almost every medical man has met with cases of this kind; but, not to multiply instances, the late Dr Thomson of Edinburgh narrated 85 such cases of second attacks of small-pox which occurred in his practice, and Heine records 57. It is vain, therefore, nay, it is silliness, to expect that the modified disease cow-pox will give greater security to the person from a subsequent attack of small-pox than small-pox itself. All that can reasonably be asked is, that vaccination shall give as great security against a subsequent attack of small-pox as if the person had passed through small-pox itself; and this, the accumulating evidence of the last sixty years most thoroughly proves that it does if it be properly performed, and with good lymph.

Of late years, in consequence of the increase of small-pox among some of the populations of Europe, the question of the protective powers of vaccination has been again keenly agitated, and a mass of most valuable information has been published by the government of this country, through the agency of the Epidemiological Society and of the Board of Trade. (See parliamentary papers, Small-Pox and Vaccination, No. 434, Session 1853; and Papers relating to the History and Practice of Vaccination, 1857.) This agitation has resulted in establishing more fully than ever the protective powers of vaccination against a subsequent attack of small-pox, and fully authorises the conclusion that vaccination, properly performed, presents almost absolute security against death by small-pox. The numerous facts collected have also demonstrated that small-pox is on the increase, not from any failure in the protective power of vaccination, but from the ignorant masses of the population, either through culpable carelessness or ignorance, rejecting its benefits. Wherever individuals have taken the trouble to ascertain, by house to house visitation, the proportion of the population actually protected by vaccination, they have expressed surprise, not that small-pox was prevalent, but that it was so rare, seeing such a large mass of the population was unprotected from its ravages. In this country the statistics of recruiting give the nearest approximation to the actual condition of our adolescent population as to vaccination, and by these it appears that 71 per cent, only of the recruits, from 1844 to 1851, bore distinct marks of vaccination on their arms, while 22 per cent. had already had small-pox, and 6½ per cent. were wholly unprotected, and ready to fall victims to the first epidemic of small-pox which should arise. If only 71 per cent, then, of the adult population is protected by vaccination, need it surprise any one that small-pox still continues a virulent disease among us? These unprotected persons not only voluntarily sacrifice their own lives, but they endanger the lives of all around them, as, if once seized with the disease, they will constitute the focus of a circle for the propagation of the disease. It is to prevent reckless or infatuated persons acting thus that various foreign governments have passed stringent laws for the enforcement of vaccination; but in this country, so great has been the dread of interfering with the liberty of the subject, that little that is effectual has been done as yet. The first great step towards this was taken by the British Parliament, in 1841, passing a legislative enactment, making inoculating with the small-pox unlawful, and encouraging the local authorities in England to provide gratuitous vaccination to the poor. It had been clearly shown that inoculation, though it diminished the chances of death to the patient, acted as a focus of infection to all around, and actually caused the general fatality of the disease to be greater than when no inoculation was practised. The act of 1841 was followed by one in 1853, rendering the practice of vaccination compulsory in England, but it also failed to secure all the benefits which a good vaccination act might have attained, through causes which need not be enlarged on. Now, however, that the public attention is fully directed to the subject, it is to be hoped that no unnecessary time will be lost in securing to England, to Scotland, and to Ireland, the benefits of a vaccination act suitable to each country.

(V.S.—K.)