fails entirely; very often produces a modified cowpox, which bears about the same relation to the genuine that varioloid does to variola, and might very properly be denominated vaccinoid; and, in a few instances, gives rise to a vesicle, which can in no respect be distinguished from the genuine. I think I have observed that a second vaccination is most effective in seasons when variolous epidemics prevail; and there is a remarkable coincidence between the vaccinoid and varioloid affections; so that the inference is perhaps justifiable, that, when a patient takes the vaccine disease a second time, he would have been more or less affected by the contagion of smallpox, had he been exposed to it. In relation to the proportion of those capable of receiving the vaccine disease more or less perfectly a second time, the annual reports of revaccinations performed in the Prussian army are highly interesting. About 40,000 soldiers have been annually revaccinated for several years; and, from a comparison of all the results, it appears that in about two-fifths of the cases "regular pustules" were produced, and in about one-fifth more "irregular pustules;" while in the remainder there was no effect whatever. If, by the regular pustule, is here meant the vaccine vesicle in its legitimate form and course, as before described, these results are very extraordinary, and far beyond anything seen in this country. If a wider extension be given to the word regular, they may not differ greatly from the effects observed among us. At all events, a singular relation is here exhibited between the proportion of persons subject to the vaccinoid disease, and of those supposed to be liable to the varioloid, which has already been stated at about one-half of the vaccinated.

The question may be reasonably asked, how it happens that the protection afforded by vaccination against smallpox is less complete than formerly. Is it owing to the wearing out of the influence of vaccination by time? Some suppose so; and they support their opinion by appealing to the fact, that children under eight years are seldom attacked. It is inferred that the preservative influence lasts about seven years. But the conclusion is not justified by the facts of the case. In the first place, it does every now and then happen that children under eight years old are attacked. Besides, vast numbers have been vaccinated at ages much beyond infancy, and it has not been observed that in these, the susceptibility to the disease returns in seven or any other given number of years. Besides, if the gradual failure of the vaccine protective influence were the law, it ought to be more general. It ought not to happen that about one-half of the vaccinated should be permanently protected, as is known to be the case. Finally, if there were such a supposed gradual wearing out of the vaccine influence, we ought to find the varioloid more and more readily produced, and more and more severe, the further it is removed from the period of vaccination, until at length it should be undistinguishable from the smallpox. Such is not the case. On the contrary, the susceptibility to the varioloid appears to diminish after the twenty-fifth year of life. The probability, therefore, is, that the supposed wearing out of the vaccine influence is imaginary. The original question then recurs; what can be the cause of the insufficiency of protection in certain cases? It may, I think, be explained by recurrence to two of the facts stated some time back; namely, the greater tendency to varioloid during the epidemic prevalence of smallpox than at other times, and its greater frequency between the ages of fifteen and twenty-five than at any other period of life. Thus, the security afforded by the vaccine disease or smallpox, occurring in seasons when no epidemic influence exists, may be effectual under similar circumstances, but may fail during an epidemic, when other forces are added to that of the contagious cause. Hence the occurrence of varioloid abundantly in Philadelphia

in 1823, though it had been previously unknown, when no epidemic influence existed. That persons are most liable to the affection between fifteen and twenty-five would seem to show that the changes which take place about the period of puberty, and continue in operation more or less until that of full maturity, which may be roughly placed at 25 or 30, are favourable to the developement of variolous disease; and that a degree of protection which might be sufficient either earlier or later in life is insufficient then.*

But, whatever may be the cause, the fact is certain, that one vaccination fails to afford security against a modified form of smallpox in very many cases; and, though the resulting affection may be in general neither fatal nor deforming, yet it is inconvenient, may become the source of a further spreading of the disease, and in some cases is very dangerous. It is important to find a remedy for these evils; and happily such a remedy is afforded in revaccination.

It is an important question, how far vaccination, performed after exposure to the cause of smallpox, is capable of preventing its occurrence, or modifying its course. So far as my observation has gone, and I believe the same result has been obtained by others, if the vaccine virus be inserted so early after exposure that the vesicle shall appear before the variolous fever has occurred, the smallpox will either be prevented altogether, or will be so far modified as to be harmless. Two cases which happened to me will illustrate this point. An infant at the breast of its mother, who was covered over with variolous eruption, was vaccinated before any appearance of the smallpox had been presented. The vaccine disease pursued its regular course, and reached its height on the ninth or tenth day; about which time some fever was observed, followed by a few abortive variolous pustules, which soon dried up without maturing, or producing any untoward symptoms whatever. A student of medicine, who had been exposed to variolous contagion, was vaccinated successfully, and just as the vaccine vesicle approached maturity, was attacked with fever followed by a moderate eruption, which dried up about the fifth day. The inference is, that vaccination should always be resorted to as soon as possible after exposure, provided the smallpox has not already commenced. It has even been asserted that, if vaccine virus be freely introduced into the variolous eruption when it first shows itself, the latter will become abortive; but experiments have not confirmed this statement.

Effects upon other Diseases.-The vaccine disease has been thought to have the power of modifying other diseases favourably, and even of superseding them. It certainly appears occasionally to set aside obstinate cutaneous eruptions. It is said to have cured various chronic inflammations, such as ophthalmia, otitis, and bronchitis. In hooping-cough, it was at one time supposed to act as a remedy; but faith in its influence over this disease has been lost. It has been employed to destroy certain erectile tumours, through the inflammation produced by the insertion of the virus; and my preceptor, the late Dr. Joseph Parrish, once employed it, with some apparent effect, in order to induce an external direction to scrofula, by inserting the lymph abundantly in the vicinity of the cervical glands. The prejudice has prevailed, to a considerable extent, that it is apt to leave a disposition to cutaneous eruptions behind it. The fact appears to be, that a lichenous, roseolous, or eczematous eruption sometimes attends the maturation of the vesicle; but this is tempo

In the report by Dr. F. W. Sargent of cases attended in the Philadelphia City Hospital, in 1845-6, it is stated that of the cases of varioloid or smallpox after one vaccination, amounting to 136, more than twice as many occurred in the ten years from 19 to 29 inclusive, as in either of the ten years preceding or following those ages. (Am. J. of Med. Sci., N. S., xvii. 372.)

rary; and the eruptions that occasionally take place afterwards are probably those which are incident to childhood, and have only an accidental relation with the vaccine disease.

Vaccination.

I shall treat of this, first, in relation to those upon whom, and the time when, it should be practised; secondly, in relation to the matter to be em ployed; and thirdly, in relation to the mode of performing the operation.

1. Persons to be vaccinated.-As new-born infants are comparatively insusceptible of the disease, in consequence possibly of the undeveloped state of their skin, the operation should generally be deferred till the sixth week or later. The third or fourth month is perhaps a still better period. It is best, under ordinary circumstances, to vaccinate only those in good health. Yet, in cases of urgency, as, for example, during the prevalence of a variolous epidemic, and especially when the individual has been exposed, or is likely to be exposed to the contagion, these precautions may be neglected, and the operation performed at once. It is easily repeated afterwards, should the vaccine disease not prove satisfactory. No particular preparation is in general required. In adult cases, however, when a plethoric or inflammatory condition of system is obvious, it may be proper to give the patient a saline cathartic, and to put him upon a reduced diet, after the insertion of the virus. It is said that the operation is more apt to fail in extremely hot, or extremely cold, than in moderate weather. It should be performed preferably in spring or autumn, other things being equal.

2. Matter employed.-The lymph taken from the vesicle on the fourth or fifth day is said to be most efficient; but it retains its virtues, little impaired, till the eighth or ninth day. After this period it deteriorates, and, if taken on the eleventh day or later, is said seldom to succeed. Infantile virus is asserted to be stronger than that of adults. When several are vaccinated from the same vesicle, those are most apt to receive the disease who come first in order.

The scab is certainly efficacious, and in this country is almost exclusively employed. It is, perhaps, rather less certain than lymph directly from the vesicle; but this is often difficult to be procured, and the scab keeps better than the dried virus in any other shape. I have used it from the commencement of my practice, and remember only two instances in unprotected persons, in which I did not sooner or later succeed with it. The scab retains its virtues for months, if preserved in a cold place; and, if at the same time excluded from the air, often continues efficacious for a year or more. It should not be carried long in the pocket, nor kept in a warm room, as it is readily decomposed by heat. When it is important to preserve it long, the scab should be thoroughly dried, then wrapped closely in tinfoil, and well coated with wax. A coating of collodion has also been recommended, in order to protect it from the air. It should be umbilicated, of a reddish-brown or garnet colour, translucent, and brittle when dry. The advice has been given to reject a thin scale formed by the drying of the pus, in the middle of the scab. In Europe, much prejudice appears to exist against the scab, which is certainly the most convenient form in which the matter can be kept, and has been found to answer every desirable purpose. In the few cases in which it fails, recourse may be had to lymph from the vesicle.

Various means of preserving the lymph have been resorted to. Sometimes it is placed, in the liquid state, between two smooth pieces of glass, where it hardens. Sometimes it is introduced into fine tubes of glass, which are then hermetically sealed. Again, threads are moistened with it, then dried, and

kept in closed tubes. It is also occasionally collected on the points of lancets, where it is allowed to harden.

In selecting matter, that should be preferred which comes from a healthy individual. Nevertheless, repeated trials appear to show that the character of the virus is not affected by any coexisting disease. The following is given as the result of the experience of M. Taupin, who has had extraordinary opportunities for ascertaining the truth. "The matter taken from children affected with acute or chronic diseases, with essential fevers, typhoid affections, eruptive fevers, thoracic, abdominal, and cerebral inflammations, the neuroses, such as chorea, hysteria, epilepsy, &c., was as energetic as if drawn from healthy children, gave rise to as copious and regular a vaccine disease, was as efficacious against smallpox, and transmitted no disease whatever, whether acute or chronic, contagious or non-contagious." (Diet. de Méd., xxx. 414.) A singular fact, also stated by M. Taupin, is, that he had on several occasions employed virus taken from children after death, but had uniformly failed, though the same cases were afterwards successfully vaccinated. (Ibid.) Á mixture of the vaccine and variolous poisons is said sometimes to produce only one disease, sometimes both, which afterwards run distinct courses.

The notion has been widely prevalent, that the vaccine matter has become deteriorated by frequently passing through the human subject. I believe, however, that there is no ground for this opinion. It is true that matter derived immediately from the cow is more powerful, and generally produces more inflammation; but there is no proof whatever that its preventive influence is in any degree the greater on this account. It is said that this greater power is speedily lost by the passage of the virus through a few successive individuals. I have been in the habit of vaccinating, and of witnessing vaccination, for more than thirty years; and, within my remembrance, there has certainly been no material change in the appearance of the local affection, as we ordinarily perceive it, or in the constitutional symptoms. If the virus has deteriorated, those recently vaccinated should be affected with varioloid more frequently and severely than those long vaccinated, which is certainly not the case. consequence of the notion just combated, recourse has occasionally been had to the cow afresh; but I believe unnecessarily; and if Jenner's opinion is true, that there are several diseases to which the cow is subject, which may be mistaken for the genuine, there may be some danger of evil consequences. A few years since, some matter was brought from Europe to this country, said to be extraordinarily efficacious. It produced, however, such violent inflammation and extensive sores, that physicians became alarmed, and I believe generally abandoned it. There is reason to believe that such matter is less efficient, as a protective agent, than that ordinarily used.

In

There would be some hazard, in the present state of our knowledge, in employing the virus which has been converted from variolous to vaccine by passing through the cow. It was stated, in most of the memoirs presented to the French Academy for their prize, that the disease produced in the cow by vaccination with ordinary vaccine matter from the human subject, is of the same mild character as in man, and that the virus undergoes no change. Others, however, came to a different conclusion; and the fact, that the matter is rendered more powerful by passing through the cow, is inferrible from thousands of experiments made in Bavaria, by direction of the government. (Watson's Lectures, 2d Am. ed., p. 1011.)

3. The Operation.-The most convenient place for the insertion of the virus is the back of the forearm, about half-way between the hand and elbow. The vesicle is in this situation least likely to be interfered with in nursing, or to be injured by tightness of the sleeves. In females, however, it is customary to

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vaccinate on the outer part of the arm, near the insertion of the deltoid; the object being to avoid an unsightly scar, in a part of the arm likely to be exposed. The plan of operation which I learned from my predecessors, and have uniformly pursued, is first to reduce the matter, if solid, to the consistence of pus, with water, upon a piece of glass; then, taking a little upon the point of a lancet, and holding the arm in the left hand so as to render the skin somewhat tense, to make three slight punctures obliquely under the cuticle, and gradually to work in the matter, till none is left on the lancet, or the surface of the skin. The punctures should be about a line apart, and at the three angles of an equilateral triangle. This number generally insures success, one taking, if the others fail; while, even if all are effective, only one pock results. Care should be taken not to draw much blood, as it is apt to wash out the virus. It is sufficient that a tinge of blood should be seen in the punctures. I have generally preferred a lancet not very sharp, as we are thus enabled to penetrate some distance under the cuticle, without causing the flow of blood.

Various other modes of operating have been recommended. I shall refer only to one in considerable vogue, which consists in making several minute superficial incisions, crossing each other, with a very sharp lancet, and then applying the matter to the wounded surface.

It has been recommended, when the skin is hard, to soften it with an emollient poultice before operating; and, when pale and inactive, to excite it by friction. These measures may be resorted to in cases of failure.

If not successful at first, the operator should make repeated trials, and, failing with matter from the crust, should have recourse directly to the vesicle. Sometimes he will succeed by postponing the second operation for some weeks or months.

Should doubt from any cause exist as to the genuineness of the disease, a good plan of testing it is to introduce a portion of virus into the other arm about the fourth or fifth day. If the disease is genuine, the new vesicle formed will correspond in its course with the original, and arrive at its height at the same time, though it will usually be smaller. If the second vaccination is performed after the sixth day, it is asserted that it fails altogether, because the system becomes by this time protected against a new impression, whether from vaccine or variolous matter. Should the test just mentioned fail, or not be resorted to, revaccination should be employed immediately, in all doubtful cases.

Treatment.-In general, little or nothing is required. Should the fever be high, and the local inflammation considerable, a saline cathartic may be given, the patient placed upon a vegetable diet, and cold water or lead-water applied to the arm. Cases sometimes occur in which the loss of a little blood from the arm is advisable; but they are rare. Great care should be taken, in the progress of the disease, that the vesicle is not broken, or otherwise injured.

ease.

Revaccination.

This operation should be employed in every case which has not been tested by exposure to smallpox contagion, during an epidemic prevalence of the disThe following are the reasons for this advice. 1. There can be no certainty that an individual, only once vaccinated, may not have an attack of modified smallpox on exposure; and, though the attack will probably be moderate, no one can predict, with confidence, that it may not be severe and even dangerous; and, at all events, it will be worse than a revaccination. 2. Abundant experience has shown that a second vaccination, properly timed, is capable of supplying any deficiency of protection left by the first, in the vast majority of cases. I have been in the habit of revaccinating for about thirty years; and, during that time, have seen no decided case of varioloid in any one that