in geometry, is used for that inequality or change which takes place in the curvature of all curves except the circle, by which their curvature is more or less in different parts of them; and this variation constitutes the quality of the curvature of any line.

**VARIOLÆ VACCINÆ**, or Cow-pox, is the name commonly, though as some people think improperly, given to a very singular disease, which, for two or three years past, has occupied a great share of the attention of medical men. It has been many years prevalent in some of the great dairy counties in England, particularly Gloucestershire; and it has been long understood by the farmers and others in these counties, that it forever exempts all persons who have been infected with it from the contagion of smallpox.

It is very surprising that, though they knew this fact, and although no person had ever been known to die of the cow-pox, they never thought of having recourse to a voluntary infection of this kind, in order to free themselves and their families from the possibility of being infected with the various poisons, which so often proves mortal. In one case, indeed, communicated to Dr Pearson by Mr Downe of Bridport, the experiment was long ago tried by a farmer upon his own person, and with complete success: But this only makes it the more wonderful that his example should not have been followed.

In the town of Kiel, however, in the duchy of Holstein, where the disease is said to be well known, as frequently affecting cows, we are told that children are sometimes inoculated with cow-pox (Die Finner), with a view to preserve their beauty; but that the people in the country do not like this inoculation, because they pretend that it leaves behind it several disorders.

With these exceptions, Dr Jenner was the first person who introduced the vaccine inoculation; and to him the public are also indebted for the first careful and accurate investigation of this interesting subject. The following is his account of the origin and history of the disease, and of its characteristic symptoms.

"There is a disease to which the horse, from his state of domestication, is frequently subject. The farmers have termed it the gout. It is an inflammation and swelling in the heel, from which illus matter possessing properties of a very peculiar kind, which seems capable of generating a disease in the human body (after it has undergone the modification which I shall presently speak of), which bears so strong a resemblance to the smallpox, that I think it highly probable that it may be the source of that disease.

"In this dairy county (Gloucestershire), a great number of cows are kept, and the office of milking is performed indiscriminately by men and maid servants. One of the former having been appointed to apply dressings to the heels of a horse affected with the gout, and not paying due attention to cleanliness, inadvertently bears his part in milking the cows with some particles of the infectious matter adhering to his fingers. When this is the case, it commonly happens that a disease is communicated to the cows, and from the cows to the dairy maids, which spreads through the farm until most of the cattle and domestics feel its unpleasant consequences. This disease has obtained the name of the cow-pox. It appears on the nipples of the cows in the form of irregular pustules. At their first appearance they are commonly of a palish blue, or rather of a colour somewhat approaching to livid, and are surrounded by an erysipelatous inflammation. These pustules, unless a timely remedy be applied, frequently degenerate into phagedenic ulcers, which prove extremely troublesome. The animals become indisposed, and the secretion of milk is much lessened. Inflamed spots now begin to appear on different parts of the hands of the domestics employed in milking, and sometimes on the wrists, which quickly run on to suppuration, first assuming the appearance of the small ulcerations produced by a burn. Most commonly they appear about the joints of the fingers, and at their extremities; but whatever parts are affected, if the situation will admit, these superficial suppurations put on a circular form, with their edges more elevated than their centre, and of a colour distinctly approaching to blue. Absorption takes place, and tumours appear in each axilla. The system becomes affected, the pulse is quickened, and shiverings, with general latitude, and pains about the loins and limbs, with vomiting, come on. The head is painful, and the patient is now and then even affected with delirium. These symptoms, varying in their degrees of violence, generally continue from one day to three or four, leaving ulcerated fores about the hands, which, from the sensibility of the parts, are very troublesome, and commonly heal slowly, frequently becoming phagedenic, like those from whence they sprung. The lips, nostrils, eyelids, and other parts of the body, are sometimes affected with sores; but these evidently arise from their being needlessly rubbed or scratched with the patient's infected fingers. No eruptions of the skin have followed the decline of the feverish symptoms in any instance that has come under my inspection, one only excepted; and in this case a very few appeared on the arms; they were very minute, of a vivid red colour, and soon died away without advancing to maturation: so that I cannot determine whether they had any connection with the preceding symptoms.

"Thus the disease makes its progress from the horse to the nipple of the cow, and from the cow to the human subject.

"Morbil matter of various kinds, when absorbed into the system, may produce effects in some degree similar; but what renders the cow-pox virus so extremely singular is, that the person who has been thus affected..." VAR [741] VAR

is for ever after secure from the infection of the smallpox; neither exposure to the various effluvia, nor the infection of the matter into the skin, producing this distemper.

"It is necessary to observe, that pustulous sores frequently appear spontaneously on the nipples of cows; and instances have occurred, though very rarely, of the hands of the servants employed in milking being affected with sores in consequence, and even of their feeling an indisposition from absorption. These pustules are of a much milder nature than those which arise from that contagion which constitutes the true cow-pox. They are always free from the bluish or livid tint so conspicuous in that disease. No erysipelas attends them, nor do they show any phlegmatic disposition, as in the other case, but quickly terminate in a scab, without creating any apparent disorder in the cow. This complaint appears at various seasons in the year, but most commonly in the spring, when the cows are first taken from their winter food and fed with grass. It is very apt to appear also when they are feeding their young. But this disease is not to be considered as similar in any respect to that of which I am treating, as it is incapable of producing any specific effects on the human constitution. However, it is of the greatest consequence to point it out here, lest the want of discrimination should occasion an idea of security from the infection of the small-pox, which might prove delusive."

Dr Jenner adds, that the active quality of the virus from the horse's heels is greatly increased after it has acted on the nipples of the cow, as it rarely happens that the horse affects his drier with force, and as rarely that a milkmaid escapes the infection when the milk infected cows. It is most active at the commencement of the disease, even before it has acquired a pus-like appearance. Indeed the Doctor is rather induced to think that the matter loses this property entirely as soon as it is secreted in the form of pus, and that it is the thin darkish looking fluid only, oozing from the newly formed cracks in the heels, similar to what sometimes exudes from erysipelasous blisters, which gives the disease. He is led to this opinion, from having often infected pus taken from old sores in the heels of horses, into scratches made with a lancet, on the found nipples of cows, which has produced no other effect than simple inflammation.

He is uncertain if the nipples of the cow are at all times susceptible of being acted upon by the virus from the horse, but rather supposes that they must be in a state of predisposition, in order to ensure the effect. But he thinks it is clear that when the cow-pox virus is once generated, the cows, when milked with a hand really infected, cannot resist the contagion, in whatever state their nipples may chance to be. He is also doubtful whether the matter, either from the cow or the horse, will affect the found skin of the human body; but thinks it probable that it will not, except on those parts where the cuticle is very thin, as on the lips.

At what period the cow-pox was first noticed in Gloucestershire is not upon record. The oldest farmers were not unacquainted with it in their earliest days when it appeared upon their farms, without any deviation from the phenomena which it now exhibits. Its connection with the small pox seems to have been unknown to them. Probably the general introduction of inoculation first occasioned the discovery. Dr Jenner conjectures that its rise in that neighbourhood may not have been of very remote date, as the practice of milking cows might formerly have been in the hands of women only; and consequently the cows might not in former times have been exposed to the contagious matter brought by the men servants from the heels of horses. He adds, that a knowledge of the source of the infection is new in the minds of most of the farmers, but has at length produced good consequences; and that it seems probable, from the precautions they are now disposed to adopt, that the appearance of the cow-pox in that quarter may either be entirely extinguished or become extremely rare.

"With respect to the opinion adduced (Dr Jenner observes), that the source of the infection is a peculiar morbid matter arising in the horse; although I have not (says he) been able to prove it from actual experiments conducted immediately under my own eye, yet the evidence I have adduced appears to establish it.

"They who are not in the habit of conducting experiments, may not be aware of the coincidence of circumstances, necessary for their being managed so as to prove perfectly decisive; nor how often men engaged in professional pursuits are liable to interruptions, which disappoint them almost at the instant of their being accomplished; however, I feel no room for hesitation respecting the common origin of the disease, being well convinced that it never appears among the cows, except it can be traced to a cow introduced among the general herd which has been previously infected, or to an infected servant, unless they have been milked by some one who, at the same time, has the care of a horse affected with diseased heels."

The following case, which we also quote from Dr Jenner, would seem to shew that not only the heels of the horse, but other parts of the body of that animal, are capable of generating the virus which produces the cow-pox.

"An extensive inflammation of the erysipelas kind appeared, without any apparent cause, upon the upper part of the thigh of a bucking colt, the property of Mr Millet, a farmer at Rockingham, a village near Berkeley. The inflammation continued several weeks, and at length terminated in the formation of three or four small abscesses. The inflamed parts were fomented, and dressings were applied by some of the same persons who were employed in milking the cows. The number of cows milked was twenty-four, and the whole of them had the cow-pox. The milkers, consisting of the farmer's wife, a man, and a maid servant, were infected by the cows. The man-servant had previously gone through the small pox, and felt but little of the cow-pox. The servant maid had some years before been infected with the cow-pox, and she also felt it now in a slight degree; but the farmer's wife, who never had gone through either of these diseases, felt its effects very severely. That the disease produced upon the cows by the colt, and from them conveyed to those who milked them, was the true and not the furious cow-pox, there can be scarcely any room for suspicion; yet it would have been more completely satisfactory had the effects of various matter been ascertained on the farmer's wife; but there was a peculiarity in her situation which prevented my making the experiment." Subsequent authors have not been all disposed to adopt Dr Jenner's opinion that this disease derives its origin from the grease in horses. We have seen the Doctor himself allow that he has not been able to prove it exclusively by actual experiments; and to establish a fact so contrary to all analogy, perhaps no weaker evidence ought to be admitted. The only other better disorder with which we are acquainted, which is capable of being communicated by contagion to the human species, is hydrophobia; but here the disorder is the same in man as in the animal from which he derives it; and the analogy holds good in the propagation of the vaccine disease from the cow to her milker. But that the discharge from a local disease in the heel of a horse should be capable of producing a general disorder in the constitution of a cow, with symptoms totally different, and that this new disease once produced should be capable of maintaining an uniform character in the cow and in man, seems a much greater departure from the ordinary proceeding of Nature. We are very far from saying that this is impossible; for little indeed do we know of what Nature can or cannot do. All we mean to say is, that a fact so extraordinary ought not to be hastily admitted.

In Holstein, we are told that the farmers do not know of any relation existing between the grease and the cow pox, at least a person who resided there three years in that country never heard of any. This, however, is certainly no proof. The same communication which contains this remark (a letter from Dr De Carro of Vienna to Dr G. Pearson) adds, "that in great farms men do not milk cows, but that in the smaller ones that happens very often; that a disease of horses, called mauke (true German name for grease), is known by all those who take care of them; that old horses particularly, attacked with the mauke, are always put in cow's stables, and there are attended by women; and that it is particularly in harvest that men in small farms milk cows." It must be allowed, then, that in this situation, supposing Doctor Jenner's opinion well founded, the cow-pox was naturally to be looked for, and here accordingly we find it. The question is certainly of no real utility, and therefore it has very properly been less attended to than other points respecting this disorder which lead to important practical conclusions.

Of all the questions which have arisen relative to the cow-pox, there is none so interesting, and luckily there is none which has received to full a discussion, or so satisfactory an answer, as the one we are now about to consider. Are those persons who have once had the cow-pox effectually and for ever secured against the variolous contagion?

Dr Jenner, in his first publication, was decidedly of opinion that a previous attack of this disorder rendered the human body for ever unsusceptible of the variolous virus; and besides the universal popular belief in the countries where cow-pox is known, he brought forward a number of cases in support of his assertion. By some of these it appeared that persons who had been affected with the cow-pox above twenty or thirty years before, continued secure against infection, either by the effluvia from patients under small pox, or by inoculation. But along with this opinion he entertained other two, which, to many people, appeared so surprising as to take away all credit from the former. The first was, that a previous attack of small-pox did not prevent a subsequent attack of cow-pox; and the second was perhaps still more wonderful, that the cow-pox virus, although it rendered the constitution unsusceptible of the small-pox, should nevertheless leave it unaltered with respect to its own action, for that the same person is susceptible of repeated attacks of the cow-pox.

These opinions have been submitted to the test of very extensive experience by a variety of intelligent practitioners; and we think there can now be little doubt that the two last are erroneous, while the truth of the first has been established by an immense body of incontrovertible evidence.

The opinions that a person who has had the small-pox may afterwards have the cow-pox, and that the same person may have the cow-pox more than once, probably arose from the distinction between the local effects of the vaccine virus, and the general disorder of the constitution not having been sufficiently attended to. It is generally admitted, that in the inoculated small-pox the local affection may go so far as that a pustule shall arise on the part, containing matter capable of communicating the true small pox to others, and yet, if no general affection of the constitution takes place, the patient is not secure from the disorder. In like manner, there are cases upon record which prove that a person may, after having had the small pox, have a local affection produced by inoculation, in which true variolous matter shall be formed capable of communicating both the local and constitutional symptoms of small-pox to others; and nurses, when much exposed to variolous contagion, often have an eruption resembling small-pox upon such parts of their skin as have been exposed to the action of the virus, though they have formerly undergone the disease. Yet there is probably no person at this day who will go so far as to assert that the same person can have the specific variolous fever more than once.

The case seems to be precisely the same with respect to cow-pox. Doctor Pearson and others have inoculated a number of persons after they have had the small pox with the vaccine virus, and have produced only the local affection; and by the same test it is ascertained that the same person cannot more than once have the constitutional symptoms of the cow-pox. Dr Woodville indeed tells us that he has seen one case of genuine cow-pox pustule and specific fever in a constitution which had previously suffered the small-pox. There can be no higher authority on this subject than that of Dr Woodville; and if he had actually seen his patient in the small pox as well as the cow pox, we should have admitted this single case as completely decisive of the question. But the only evidence of this person having had the small pox, is the assertion of the patient that he had it when a child. This we can by no means sustain as conclusive in opposition to the Doctor's own experience, as well as the experience of Dr Pearson.

That the milkers are subject to repeated attacks of the local symptoms of cow pox, whether they have had the small-pox or not, is certain. In the case of the farmer's servants at Rockhampton, which we have quoted above from Dr Jenner, one of whom had previously undergone the small pox, and the other the cow-pox, and both of whom were afterwards infected by VAR

By the cow-pox in a flight degree, it seems reasonable to conclude that the local symptoms only were present in the last attack. We may at the same time observe, that in a case of this kind, where a very painful ulcer is produced in a very sensible part, this may probably be attended by an increased frequency of pulse; yet if this has not the specific marks of the cow-pox fever, we should not say that such a person has the disorder constitutionally.

With respect to the principal proposition, that the specific fever of cow-pox renders the constitution unsusceptible of the variolous fever, we think no doubt now remains. Above 1000 persons who have undergone the vaccine inoculation have been afterwards inoculated with variolous matter, which has produced no other than local effects. Besides these, there have been a vast number inoculated by private practitioners in different parts of the kingdom, the result of which has not been reported. But we may safely suppose, that if any one of them had afforded a conclusion opposite to the one now generally admitted, it would have been communicated to the public.

We must not, however, conceal one seemingly well authenticated case which has lately occurred, and which, so far as it goes, certainly militates against this conclusion, and which, we doubt not, will be eagerly caught at by the opponents of the new practice. We quote it from the Medical and Chirurgical Review for September 1800.

"Mr Malin, surgeon of Carey Street, London, inoculated a child, two years and an half old, with vaccine matter procured from Dr Jenner. On the third day there were sufficient marks of the action of the virus, and from this time to the end of the disease the local affection proceeded regularly and without interruption. On the eighth day the child complained of headache and sickness; had a quick pulse, white tongue, and increased heat, with an enlargement and tenderness in the axilla. These symptoms subsided in the course of the next day, and the child remained well till the twelfth, when it had a very severe attack of fever, succeeded, the following day, by an eruption; the appearance, progress, and termination of which, left no doubt in the minds of several eminent practitioners of its being the small-pox. That it was really so, has been since clearly proved by inoculation. There was a child ill of small-pox in the house at the time the above inoculation for cow-pox was performed."

The Reviewers justly remark, that the history is defective, in not describing more minutely the appearances of the inoculated parts at the different stages, as well as in not mentioning the length of time that the matter had been taken previous to being used. Both these points are the more important, as a suspicion naturally arises, that the local affection which succeeded the vaccine inoculation was not the genuine cow-pox pustule, but one of the spurious kind, which had not the power of destroying variolous susceptibility. The matter having been furnished by Dr Jenner, no doubt, renders this supposition the less probable; but if it was either long or improperly kept after it came out of his hands, it may have undergone a material change, by putrefaction or otherwise. Dr Jenner mentions an instance of a practitioner, who had been accustomed to preserve variolous matter in a warm pocket; a situation favourable for producing putrefaction in it. This matter, when infected, was found to produce inflammation, swellings of the axillary glands, fever, and sometimes eruptions; but not of the true variolous kind, as patients thus inoculated were found still susceptible of the small-pox contagion. It is merely a possible supposition, that merely a conjecture, that the vaccine matter in Mr Malin's case had undergone some such change.

The case however, is in several respects an interesting one. As it has been supposed that variolous contagion, communicated in the form of exhalation, does not affect the constitution in less than fourteen or fifteen days, and as the vaccine matter, communicated by inoculation, produces its specific effects some days earlier, it has been suggested, that wherever a person has been accidentally exposed to variolous effluvia, we should endeavour to anticipate the small-pox by immediately inoculating with the vaccine virus. But if there be nothing fallacious in the above case, it appears that this measure would not stop the progress of the small-pox, but that our patient would incur the additional danger of having two diseases instead of one.

At all events, it must be allowed that this child had probably been infected by the small-pox before the vaccine matter had begun to produce its specific effects, and probably even before the inoculation. Thus the small-pox may be considered as having begun before the cow-pox; and though we should be forced to allow that, matters being thus situated, the latter disorder could not prevent the further progress of the former, it by no means follows, that when the cow-pox has fairly run its course, the constitution is still susceptible of small-pox. The two diseases must have existed in this patient at the same time, though the one was in a latent state during the active stage of the other.

This solitary case, then, is by no means conclusive, and certainly is not sufficient to outweigh the immense mass of concurring evidence which is opposed to it.

We proceed now to another highly important branch of our subject—the comparison of the advantages and disadvantages of the two diseases, with a view to the new practice of inoculation.

Notwithstanding the immense number of cases in which the inoculation of the cow-pox has been tried, we are not yet fully qualified to appreciate the value of the new practice; because the disease has varied very much in severity, and even in its most remarkable symptoms, and that without any cause which has yet been discovered.

Dr Jenner's account of the disease gave us reason to think that the local affection in cow-pox was more severe than in the inoculated small-pox: That the fever in this disease was never attended with dangerous symptoms: that those symptoms which affect the patient with feverity are entirely secondary, excited by the irritating processes of inflammation and ulceration: that the disease was not attended with any eruption resembling small-pox: and that the force produced by the inoculation was apt to degenerate into a very dilapidated phagedenic ulcer, which required to be treated with applications of a caustic nature, of which he found the unguentum hydrargyri nitratii the most useful.

Soon after Dr Jenner's publication, the attention of medical men was forcibly drawn to the subject; and several eminent practitioners in London, particularly Dr George... George Pearson, and Dr Woodville physician to the smallpox and inoculation hospitals, immediately began to practise the vaccine inoculation. The latter gentleman from published an accurate and candid account of the effect of this virus upon 200 patients, with a table of the results of above 500 cases in which the inoculation was performed.

It is very remarkable, that in none of these cases did the inoculated part ulcerate in the manner described by Dr Jenner, nor did the inflammation ever occasion any inconvenience, excepting in one instance, in which it was soon subsided by the aqua lithargyri acetatis. The general affection of the constitution, on the other hand, though in a great majority of cases it was very slight, yet, in some instances, was severe. An eruption, exactly resembling small-pox, was contrary to expectation, a very common occurrence, and in some the pustules were not fewer than 1000; and although in these cases the disease was still attended with secondary fever, yet the febrile symptoms which took place from the commencement were considerable, and even alarming, as sometimes also happens with the inoculated small-pox.

Dr Woodville sometimes inoculated with matter from the primary sore in the arm, and sometimes with matter taken from the pustular eruption; and it appears from the table that a much larger proportion of those who were inoculated in the latter way had pustules, than of those who were inoculated either with matter immediately from the cow, or from the primary sore in the human body. There were 447 patients in all inoculated, either from the cow or from the primary sore; and of these 241 had pustules, and 206 had none. Sixty-two persons, on the other hand, were inoculated with matter from the pustules of ten different patients; and of these no fewer than 57 had pustules, and only 5 escaped without. Nor can it be said that this disproportion arose from these 10 patients having the disease in a more virulent form than ordinary, for matter was also taken from the primary sore in 4 of the 10, with which 48 were inoculated; of whom 27 had pustules, and 21 had none; whereas, of 9 persons who were inoculated with matter from the pustules of these same 4, only 2 escaped without pustules. This observation corresponds also with Dr Pearson's experience.

Although these eruptions have been met with by other practitioners, yet they certainly appear very rarely in private practice. Dr Woodville, for this reason, considers them, in a more recent publication, as the effect of some adventitious cause, independent of the cowpox; And this he supposes to be the variolated atmosphere of the hospital, which those patients were necessarily obliged to inspire during the progress of the cowpox infection. This opinion, however, does not seem to agree well with his former remark, which, as we have said, is confirmed by Dr Pearson, that eruptions rarely took place, if care was taken to avoid matter for inoculation from such as had pustules; a fact that cannot be explained on such a supposition. Neither is this idea reconcilable with what he also tells us, that the proportion of cases in the hospital attended with pustules has been of late only three or four in a hundred.

This change in the appearances of the disease in the hands of different practitioners, and even of the same practitioner at different times, is one of the most unaccountable circumstances respecting this singular disorder. There is some curious information on this subject, contained in a letter from Mr Stromeyer of Hanover to Mr Hahnemann.

"This year (says he) we have inoculated 40 persons, as well with the vaccine matter received of Dr Pearson as with that from Dr Jenner; all of whom underwent the disease properly.

"Between the London and Gloucester vaccine matter, it appears to me there subsists an essential difference. The London matter produces frequently an eruption of small pimples; but they disappear within a day or two at farthest. Dr Pearson calls these eruptions pusules.—The Gloucester matter has never produced this effect here; but frequently occasioned eruptions of the inoculated part, of a tedious and long duration; which the latter never did so; on account of which I now only make use of Dr Pearson's vaccine matter. The nettle-fever-like eruptions I have observed several times, but never that sort of eruption, repeatedly noticed in London, which so much resembles the small-pox."

If these observations of Mr Stromeyer should be confirmed by the experience of others, they would go far to explain the difference which the London practitioners have found in this disease from the account given of it by Dr Jenner, notwithstanding the absence of the eruption resembling small-pox at Hanover. We believe an interchange of vaccine matter has once or twice taken place between London and Gloucestershire. Is it since that period that the eruption has been less frequent at London? Dr Pearson is inclined to suppose, that the comparative severity of the disease at London, during the first winter, arose rather from the difference in the human constitution at the different seasons of the year, than from any change in the state of the vaccine matter.

In comparing the degree of danger from the inoculation of cow-pox with that arising from the inoculated practice for the old small-pox, we are convinced that Dr Pearson greatly overrates the mortality in the latter disorder. He supposes it to be no less than one in 200. Dr Muffley, on the other hand, who is a violent opponent of the vaccine inoculation, affirms, that he has inoculated several thousands with various matter, in Europe and the West Indies, without ever losing a patient, and that several other persons, whom he knows, have done the same, with the same success. We are afraid, however, that the experience of other inoculators does not afford a favourable result. We believe that in this country the mortality is often occasioned by improper treatment; and from comparing the accounts which we have received from practitioners of extensive experience, and undoubted veracity, we believe that, where the treatment is proper from the beginning, the symptoms very rarely arise to an alarming height, and that the mortality is not so great as one in 600. And this estimate nearly corresponds with Dr Woodville's very great experience. It must be allowed, that patients in an hospital are subject to many disadvantages, which may be avoided in private practice; yet, out of the last 3000 cases of various inoculation at the inoculation hospital, prior to the publication of the Doctor's reports, the mortality did not exceed one in 600.

Notwithstanding this statement, however, we are hap- The local tumor produced by the inoculation of the cow-pox is commonly of a different appearance from that which is the consequence of inoculation with variolous matter; for if the inoculation of the cow-pox be performed by a simple puncture, the consequent tumor, in the proportion of three times out of four, according to Dr Woodville, assumes a form completely circular, and it continues circumscribed, with its edges elevated and well defined, and its surface flat, through every stage of the disease; while that which is produced from the variolous matter, either preserves a peculiar form, or spreads along the skin, and becomes angulated, or irregular, or disfigured by numerous vesicles.

Another distinction still more decisive and general, is to be drawn from the contents of the cow-pox tumor; for the fluid here formed very rarely becomes puriform; and the scab which succeeds is of a harder texture, exhibits a smoother surface, and differs in its colour from that which is formed by the concretion of pus. The appearances, however, are sometimes so changed, that they can in no respect be distinguished from those which arise from the inoculation of small-pox. We may also mention that the tendency of the sore in the inoculated part to degenerate into a phagedenic ulcer does not occur in small-pox.

On the other hand, the points in which these two diseases resemble each other are very remarkable. When introduced into the body by inoculation, they affect the constitution in nearly the same length of time, and seem to be governed by nearly the same laws. They mutually destroy the susceptibility of the body for the action of each other.

Dr Pearson, who thinks the diseases ought to be considered as distinct species, nevertheless draws the following conclusion, as established by experience:

"That in certain constitutions, or under the circumstances of certain co-operating agents, the vaccine poison produces a disease resembling the small-pox; and of course the pustule in the inoculated part is very different from that of the vaccine pox ordinarily occurring, and the eruptions resemble very much, if not exactly, some varieties of the small-pox."

That in some instances these eruptions have occurred, although the inoculated part exhibited the genuine vaccine pustule; that the matter of such eruptive cases, whether taken from the inoculated part, or from other parts, produces universally (a), or at least generally, similar eruptive cases; and has not (he believes) been seen to go back, by passing through different constitutions, to the state in which it produces what is called the genuine vaccine disease; that eruptions, of a different appearance from variolous ones, sometimes occur in the true cow-pox."

From these facts we are strongly inclined to think that the vaccine disease and the small-pox ought merely probably to be considered as varieties of the same disease; and we have little doubt that they both derive their origin from the same source.

If Dr Jenner's opinion, that the vaccine disease is derived from the grave, were fully established, we should be disposed to offer a conjecture, that the small-pox, in coming from the horse to man, may have passed thro'

(a) We have seen that Dr Woodville's table contains a few exceptions to this rule; though it strongly confirms the general truth of the proposition. Vaccination

Some animal different from the cow, and may thus have undergone a modification similar to, but not exactly, the same with what takes place in the passage of the virus through the constitution of the cow.

But without having recourse to this conjecture, which is perfectly gratuitous, we are of opinion that the variations which have taken place in the cow pox within the last three years are sufficient to warrant a belief, that the small-pox may have originally been exactly the same disease, even in the human constitution, as the cow-pox is now; but that in a succession of ages, and from the operation of causes wholly unknown to us, it may have been changed to what we now see it.

We shall now conclude this article with a few practical remarks, which we hope may be of use to practitioners who mean to begin the vaccine inoculation.

It is of the utmost consequence that the matter employed should be the genuine vaccine virus. Dr Jenner points out the following particulars as sources of a spurious cow-pox: 1. That arising from pustules on the nipples or udder of the cow, which pustules contain no specific virus. 2. From matter, although originally possessing the specific virus, which has suffered a decomposition, either from putrefaction, or any other cause less obvious to the senses. 3. From matter taken from an ulcer in an advanced stage, though the ulcer arose from a true cow-pox. 4. From matter produced on the human skin from the contact of some peculiar morbid matter generated by a horse.

Many have remarked, that inoculation with the vaccine matter is more apt to fail in communicating the infection than with variolous matter, especially if it be suffered to dry upon the lancet before it is used. This does not seem to depend upon the virus of the former being more volatile, but upon its becoming more hard and indissoluble upon evaporation. Care should therefore be taken to moisten it a considerable time before it is used.

We have already noticed the danger that may arise from mistaking the local effects of the vaccine disease for its effects upon the constitution. To guard practitioners against this error, Dr Woodville makes the following remarks: "When a considerable tumor and an extensive redness take place at the inoculated part, within two or three days after the infectious matter has been applied, the failure of inoculation may be considered as certain as where neither redness nor tumor is the consequence. This rapid and premature advancement of the inflammation will always be sufficient to prevent the inoculator from mistaking such cases for those of efficient inoculation. But there are other circumstances under which I have found the inoculation to be equally ineffectual, and which, as being more likely to deceive the inoculator, require his utmost circumspection and discrimination. I here allude to cases in which it happens that though the local affection does not exhibit much more inflammation than is usual, yet neither vesicle nor pustule supervenes; and in which, about the sixth or seventh day, it rapidly advances into an irregular suppuration, producing a festering or crustaceous sore. Care, however, should be taken to distinguish this case from that in which the inoculated part assumes a pustular form, though it continues for one or two days only, when the same appearances follow as those above described; for I have experienced the latter inoculation to be as effectual as where the tumor has proceeded in the most regular manner."

"The efflorescence at the inoculated part, which seldom intervenes before the eighth, or later than the eleventh, day, is to be regarded as an indication that the whole system is affected; and if the patient has not felt any indisposition on or before its approach, he may be assured that there will not be any afterwards. When efflorescence does not commence till the eleventh day, it is almost always attended with more indisposition than when it occurs on the eighth or ninth day. The efflorescence is more frequent in young infants than in children advanced to three or four years of age; and the former have the efflorescence and the disease more favourably than the latter, insomuch that by far the greater part of them have no perceptible illness, and require no medicines. On the other hand, in adults, the cow-pox frequently produces headache, pain of the limbs, and other febrile symptoms, for two or three days, which are greatly relieved by a brisk purgative."

We would, upon the whole, recommend the vaccine inoculation to our medical readers as being an effectual preventative against the small-pox, and safer to the individual, while it is more advantageous to the public at large, in being less capable of propagation by contagion.