its influence, will become impaired by time, but simply as a test whether the liability of the individuals to variolous disease has been fully overcome.

Revaccination, as is well remarked in a report to the Belgian Academy of Medicine, in 1858, is the useful and indispensable complement of a first vaccination. Not that it is always absolutely neces sary, but that by its result we may become certain that all suscepti bility to the occurrence of variola has been extinguished. If the revaccination succeeds, we have a right to believe that protection against the infection of smallpox is in this manner confirmed. If it fails, it should be repeated at intervals more or less distant, so that we may be assured by these test vaccinations, of the entire immunity of the subject from variola.

Had we no other proof of the importance of revaccination, that derived from the results of the operation among the soldiers of the Prussian army would be sufficient. The whole army now enjoys an almost entire immunity from the contagion of smallpox, notwithstanding it has been repeatedly subjected to its influence. To the report for 1841, we find attached the following important statement: The powerful influence of revaccination, in the diminution of variolous diseases, at the different military hospitals, is most remarkable. During the year 1841, there occurred but 50 cases, of which 10 were genuine variola, 24 modified smallpox or varioloid, and 16 varicella. Three of the patients died; of these, one had not been vaccinated on his admission into the army, but his certificate indicated that he had been a short time previously; the second occurred in a recruit who had not been revaccinated; and the third, in a non-commissioned officer, who had been revaccinated some years before, but without success. Before the order for revaccination was issued, the different barracks used to be a prey to varioloid disease, which has now almost entirely disappeared.

During the nineteen years ending with the 31st December, 1852, the number vaccinated upon their entrance into the army was 811,402. The first vaccination was successful in 414,595; of the remainder, on being subjected to revaccination, in 42,986 the operation was successful; vaccination therefore took effect in a regular manner in 457,581 cases. Of these, during nineteen years, 217 were attacked with varicella, 191 with varioloid, and 13 with variola. Of the latter, four died.

Dr. Schilling very properly remarks (Viertel Jahrsschr. f. gericht. und öffent. Med. 1854) that those in whom revaccination is successful are not to be considered invariably as having been susceptible to the variolous infection. The statistics of vaccinations performed in the Prussian army show that such is not the case.

A few years since a prize was offered by the Academy of Sciences of France, for the most satisfactory essay in reply to certain queries relating to the preservative power of vaccination, the necessity of renewing the vaccine virus from the cow, and the necessity of revacci nation. The various essays sent in by the competitors for the prize

were referred to a committee of the Academy, whose report submitted in February, 1845, concludes with the following general summary deduced from the facts presented by the authors of the essays.

1. The preservative power of vaccination is absolute for the majority, and temporary for a small number: even in the latter it is absolute until adolescence. (A position also affirmed in the report on vaccination made in 1858 to the Belgian Academy of Medicine.)

2. Smallpox rarely attacks those who have been vaccinated in infancy before the age of ten or twelve; from which age, however, until thirty or thirty-five, the vaccinated are particularly liable to small-pox.

3. In addition to its protective power, vaccination so modifies the animal economy, that, even should a subsequent attack of small-pox occur, its symptoms will be rendered milder, and its duration curtailed, and its danger considerably diminished.

4. Vaccine matter taken directly from the cow causes local symptoms of greater intensity, while its effects are also more certain than those of old vaccine matter, but after being transmitted for a few weeks through the human subject the local intensity disappears.

5. The preservative power of vaccine matter does not seem to be absolutely in proportion to the intensity of the local effects produced. It is, nevertheless, prudent, in order effectually to obtain its protective power, to procure new matter from the cow as frequently as possible. 6. Revaccination is the only known method of distinguishing those of the vaccinated who remain protected, from those who do not.

7. Successful revaccination is not a certain proof that the person in whom it succeeds was liable to contract smallpox. It merely establishes a strong presumption that they were more or less liable.

8. As a general rule revaccination should be practised after the first fourteen years, but sooner during the prevalence of an epidemic of smallpox.

At a recent meeting of the London Epidemiological Society, Dr. Waller Lewis read a highly interesting and valuable paper on the Relations of Vaccination and Inoculation to Smallpox. From the facts and cases adduced by him the author drew the following general conclusions, which correspond with those at which we had previously arrived from the results of our own observations.

Vaccination is a most eminent protection against smallpox. When perfectly performed it is equally, and, in some instances, more protective than inoculation or natural smallpox. It appears to render some exanthemata, as, for example, measles, milder than they would otherwise have been. Neither vaccination, inoculation, nor smallpox, guarantee the individual in every instance from smallpox. Smallpox has been known to attack the same individual three times, or oftener. There are certain individuals who possess a perfect immunity from infection by vaccination, inoculation, or the contagion of smallpox. Great susceptibility to, or, perfect immunity from smallpox, is sometimes found to be common to several members of the same family. Sanatory conditions have a very powerful influence upon the spread of smallpox in common with other epidemics.

Dr. Lewis lays down the laws which regulate the apparent myste. ries of smallpox as follows:

Smallpox is a disease to which almost every person is liable once in his lifetime unless protected. But there is a small fraction of the community who appear to enjoy an exemption from this law, neither vaccination, inoculation, nor any degree of exposure to casual smallpox, causing them to take either vaccinia or variola. On the other hand there is a certain portion in exactly the opposite condition—individuals who are eminently susceptible to the disease. To this class belong those persons who have repeated attacks of variola; who take smallpox after having been inoculated or vaccinated. For such there is no safety but in repeated vaccination. Between this latter class, and that favored portion of the community that possess perfect immunity, there exists every shade and degree of susceptibility.

These laws explain the apparent inconsistency in the views held respecting the protective powers of vaccination. Thus, all those individuals, forming an enormous majority of mankind, who possess only a moderate degree of liability to smallpox, are completely guarded against the influence of smallpox virus, by a successful vaccination or inoculation, or by a previous attack of smallpox; while others, who have a greater susceptibility, will be absolutely protected by neither one nor the other.

It is to be recollected that the protection afforded by vaccination is fully equal to that derived from inoculation-the former is, however, unattended with any danger to the patient, and does not, like the latter, tend to keep alive and propagate a loathsome and destructive disease. At the Royal Military Asylum, it has been shown by Dr. Balfour, that 6.15 in every 1,000 boys admitted, protected by previous smallpox, and 7.06 in every 1,000 boys protected by vaccination, were attacked subsequently by smallpox. The deaths from secondary smallpox amounted to 2.05 per 1,000 of those attacked, while not a single fatal case occurred in those attacked with smallpox after vaccination. (Medico-Chirurg. Trans., 1852.) From records kept at the Smallpox Hospital, Mr. Marston proves, that the mortality from smallpox in persons well vaccinated, and who have more than two cicatrices, was less than 1.5 per cent. In those reputed to have been vaccinated, it was not more than 3 or 4 per cent., under favorable, and not more than 7 under unfavorable circumstances, while the mortality from natural smallpox varied from 20 to 35 per cent. (Medico-Chirur. Trans., 1853.)

Phenomena of Vaccination.-On the third day after the insertion of the matter in the arm, there appears, at the point where the matter was inserted, a red and slightly elevated papula, which, on the fourth day, is surrounded by a very faint and narrow inflamed base, or areola. By the aid of the microscope, the efflorescence surrounding the inflamed point will be distinctly visible. On the fifth day the cuticle is elevated into a pearl-colored vesicle, filled with a small quantity of perfectly transparent fluid. The form of the vesicle is circular or oval, according to the manner in which the introduction of the virus.

is effected. The vesicle is somewhat flattened, and with a small depression in the centre, rather darker than the rest of its surface. It continues to enlarge in circumference, but not so much in elevation, until the eighth day, when it is at its height. Its margin is then turgid and prominent, and it contains a greater or less amount of fluid. When closely examined, the vesicle exhibits a cellulated structure. By the floor of the cells, which are from ten to fourteen in number, is secreted the specific matter of the disease.

Between the eighth and ninth days, some degree of febrile excitement very generally occurs:-the glands of the axilla become, in some cases, swollen and painful, and a state of general lassitude and drowsiness, with slight creeping chills, alternating with flushes of heat, is observed. In other cases, the febrile excitement is much slighter, and, in many instances, scarcely perceptible.

On the evening of the eighth day, the slight circle of inflammation, which surrounds the vesicle on its first formation, begins to spread, until, by the tenth day, it forms a broad areola, surrounding the vesicle, of a bright red color, and of a perfectly circumscribed, circular form:. the parts occupied by it being tense and painful. By the eleventh day, the depressed centre of the vesicle begins to assume a darker hue, and this darkness gradually extends towards the circumference. By the fourteenth day, the entire surface of the pock is converted into a dark brown scab. By degrees this becomes harder and of a darker color; in a few days it begins to separate at the circumference, but still adheres at the centre, and does not fall off until between the eighteenth and twenty-first day; sometimes even later; leaving, upon its separation, a cicatrix of a form and size proportioned to the previous inflammation, and marked with radiations and indentations.

In a few instances the vesicle is developed at a somewhat earlier period; in other cases, a number of days elapse, after the insertion of the matter, before the appearance of the vesicle. According to Dr. Gregory, the period of retardation never exceeds sixteen days. It not unfrequently happens, that on the day after the matter is inserted, considerable inflammation and swelling occur at the place of insertion, which after continuing for a day or two, subside rapidly without leaving any local affection.

Most commonly but one vesicle is developed at the point where the matter is inserted; occasionally, however, one or more smaller vesicles appear in the immediate vicinity of the primary one; instances have occurred, in which numerous vaccine vesicles presented themselves on different parts of the body, the matter taken from which communicated the disease to other persons, as effectually as that derived from the primary vesicle on the arm. (Report of the Central Vaccine Committee of France, for 1818-19.)

In many cases, the wound made by the insertion of the matter becomes, at an early period, very red and itching, and a small acuminated, conoid pustule occurs on the eighth day, surrounded by an imperfect, irregular areola. The pustule is filled with an opaque, straw colored fluid, and forms a small, light-colored scab, which separates prematurely. Such cases are always to be regarded as instances

of doubtful vaccination. In other instances, instead of a circumscribed areola, an inflammation of an erysipelatous character extends over the whole arm, from the elbow to the shoulder:-the vesicle, in place of being converted into a hard scab, causes a large ulcer, which discharges profusely, and is occasionally difficult to heal: the resulting scar is large and irregular, without either radiations or pittings. In these cases, also, there is a doubt whether the system is placed fully under the influence of the vaccine infection. Another irregularity is, when, about the sixth or seventh day, the vesicle becomes partially inflamed and scaly, and surrounded by a species of psoriasis in place of an areola.. This is an unquestionable indication of spurious vaccination.

Between the ninth and twelfth day, in robust, plethoric children, it sometimes happens that the body becomes generally or partially covered with a papular eruption, which, however, in no degree interferes with the effects of the vaccination.

Period for Vaccination.-Not a little discussion has recently taken place, as to the proper age for the performance of vaccination. By some, its postponement until after the child is one year old, is strongly insisted on, under the supposition that, previously to this age, the infection of the system is apt to be imperfect, or, at best, not permanent. Others have considered the disease to be more regular, and accompanied with less febrile irritation, in infants from two to six months old; while others again maintain that it may be performed immedi ately after birth, and that it succeeds equally well at whatever age the matter is inserted.

At a discussion upon this subject before the Medico-Chirurgical Society of London, Dr. Gregory gave it as his opinion, that, provided a good vesicle and areola were produced, with a due degree of constitutional effect, it matters not whether vaccination be performed at the second or third month, or the second, third, or fourth year. He considered the true question for consideration to be, at what period of infantile life vaccination can be practised, so as most certainly to insure success, and avoid inconvenience to the parties. In the first week or ten days after birth, before the infant has attained any degree of plumpness, it is very difficult to vaccinate, not from any want of sus ceptibility in the patient, but from the difficulty of inserting the lymph properly. This difficulty is more or less present until about the fourth. month, and hence, this latter is the period usually chosen; for not only is the arm then generally plump, but there are, also, no contending influences, such as teething, present. Mr. Ceely agreed, in the main, with Dr. Gregory. It was stated by Dr. T. Thompson, at a discussion before the Medical Society of London, that at the Foundling Hospital, Paris, all the children were vaccinated within the month, and the operation was generally successful.

That vaccination performed at a very early period of infancy is not more liable to be attended with serious or disagreeable consequences than when it is postponed until the third, fourth, or sixth month, we have the concurrent testimony of Husson, Lugroux, Behier, Ragaine, Laforgue, Godefroy, Robert, Danijeut, and Depaul. (See Monit. des Scienc. Méd. et Pharm., Feb. 1862.)