of professional opinion is now conclusive that these cases were due to the admixture of syphilitic blood, or some of the inoculable products of syphilis direct from a syphilitic vaccinifer, or indirectly through the medium of syphilis infected instruments or articles, or individuals.

The practical points are: That the vaccinator should assure himself of the perfect health of the source of his vaccine virus, and of the subject to whom it is applied; that at least the same care be exercised in its application as would obtain to guard against the communication of any other disease in any other surgical operation; and that parents be cautioned against the indiscriminate handling, kissing and caressing of their children by strangers, not only during the vaccinal process, but at all times-to say nothing of exercising proper care and supervision in the selection of nurses and other attendants.

Of more practical importance than the foregoing, in the estimation of the sanitarian, are the questions as to the relative protective powers of humanized and of bovine virus; the character of the immediate results produced by each with respect to severity of constitutional disturbance and local trouble; and the promptness of action in the face of exposure. On the last two points the expressions of opinion, by those who are practically familiar with both, is decidedly in favor of humanized virus. With this, as a rule, the febrile symptoms are milder; there is less local irritation, itching, heat and tenderness; inflammation of the cellular tissue is not so severe and extensive, nor do the glands become so seriously involved; ulceration and loss of substance, abscesses, neoplasms, and the attendant eruptions, are less frequent and less serious. In addition to this, humanized virus may be depended on much more certainly than bovine to act promptly. Usually on the second or third, very seldom so late as the fourth, day after the insertion of good humanized virus, the papular stage of vaccination will begin; and be followed, with almost unvarying regularity, by complete development of the vesicle on the eighth day, and by the subsequent appearance of the "index of safety"-the specific inflammation of the skin, or stage of areola. Bovine virus, on the contrary, is subject to all degrees of delay, even up to periods of weeks. During the recent epidemic this defect of bovine virus was more than once followed by serious consequences. Not alone were lives lost among the exposed members of isolated families, where vaccination was resorted to early enough to have averted an attack, had the virus acted promptly; but epidemic outbreaks followod under similar circumstances-that is, in localities where, upon the discovery of the first case, vaccination of all unprotected or exposed was at once resorted to, with bovine virus, but which either proved so tardy in its action, or so totally inert, as to allow the disease to gain a foothold. See Details of Local Outbreaks, passim, for such instances.

"The loss of a day," says Seaton in his Hand-book of Vaccination, "may be the loss of a life." Hence the necessity for using virus which will act promptly, and not remain latent three, five or any other number of days. Recent experience corroborates observations made during the period from 1866 to 1873, while Sanitary

Superintendent of the city of Chicago, to-wit: That it is never too late to vaccinate after exposure, short of the actual appearance of the variolous eruption. If the vaccination be performed within three or four days after exposure, and the areolar stage, the index of safety, be reached in the normal time, an attack of small-pox will almost invariably be averted. With every additional day's delay the protective power will be weakened; but, contrary to the opinion laid down in text-books, experience proves that this protective power is not entirely exhausted until the vaccination is deferred at least up to the beginning of the febrile stage of small-pox. Of 323 cases of small-pox, tabulated in the preceding pages, in which the patients had never been vaccinated until after exposure, 305 recovered and 18 died, being a less mortality rate than among the 690 cases which occurred among those who had been vaccinated before exposure only. In some of these cases vaccination was not attempted until shortly before the beginning of the eruptive stage. A reference to the Notes appended to the Tabular Statement of 1,100 Cases, pages 296-327, inclusive, will show many instances where vaccination after exposure was successfully resorted to after the expiration of the period ascribed by Marson, Seaton and others, as the limit beyond which, "whatever the local success of the vaccination, no constitutional effects will be imparted." In these Notes will also be found the details of cases where the attempt to vaccinate with bovine virus was only successful after one or more repetitions, with loss of valuable time, or where such attempt finally proved wholly unsuccessful. With the exception of one group of six cases-a family vaccinated by the father, a layman-all the vaccinations performed with humanized virus after exposure, were successful and the patients recovered, with mild attacks of short duration. But of such vaccinations with bovine virus, over forty per cent. were failures that is, in the sense of manifesting activity before the variolous disease began-and of this forty per cent. of failures there was thirty per cent. of fatal results.

Moreover, it has now come to be understood that vaccination has a positive therapeutic value, as well as prophylactic power. And where it is too late to exert the latter, there may still be sufficient time to make the former available, provided the virus used act promptly. Thus, if a patient be vaccinated during the febrile stage, and the vaccination progress normally-there being nothing antagonistic between the two diseases, variola and vaccinia, to prevent such normal progress-the areolar stage of vaccination will be reached before the dangerous tenth day of the variolous disease; and, as has been repeatedly witnessed, the graver disease will be aborted, jugulated, or materially modified. As a concrete illustration of this abortive power of vaccination the following instance, which has been almost exactly paralleled in the recent epidemic, may be here cited: Of three children, equally exposed to a case of small-pox at the same time, one has been vaccinated and the other two are unprotected. The former escapes entirely; but, after the usual period of incubation, both the latter exhibit symptoms of small-pox. One of these is at once vaccinated on the appearance of these symptomsthat is, in the febrile stage; but the other remains unprotected. The disease seems equally severe in both up to the eighth or ninth

day, when the vaccinated child begins to improve; the pustules dry up, no secondary fever follows, and in a few days the patient is dismissed, convalescent. In the unvaccinated child, the disease runs the usual course of unmodified small-pox, and during the tenth to twelfth days-the period of greatest mortality, and when the other child is entirely out of danger-this one has about equal chances for and against recovery. An added significance is given by these facts to the choice of humanized virus in all cases of emergency. Under ordinary circumstances, as when vaccinating in the absence of an epidemic or of known or suspected exposure, and when time is not essential, these considerations will, of course, have less weight; but they are of sufficient importance to be better known and understood than experience shows them to be.

Concerning the sole remaining point which should influence in the decision of the choice between humanized and bovine virus-that is, the question of protective power-it will simplify the discussion if, remembering that humanized virus is admitted to have "succeeded admirably in retaining its power for the first twenty-five years of its use," it be further remembered that bovine-virus vaccination was only introduced so lately as 1866 in Europe, and 1870 in this country; and that, therefore it is, as yet, too soon to pronounce upon the absolute protective power of bovine virus. It is probable that such virus is fully as protective as humanized virus; but that it is any more so cannot properly be claimed until it has been submitted to the same tests as the latter. It may, however, be freely admitted that, if other things were equal-as to promptness of action, uniformity of results, mildness of symptoms, and degree of protective power-bovine virus has-in addition to the moral advantage arising from the popular belief in its harmlessness as regards other diseasestwo other important merits, to-wit, certainly of supply, and freedom from possibility of deterioration of whatever degree of protective power it may ultimately be found to possess. This certainty of supply will always make bovine virus desirable, especially in this country, where, in the absence of a compulsory vaccination system, or of State or other provision for maintaining an adequate supply of humanized virus, there is constant danger of a vaccine famine, such as was experienced in many localities during the recent epidemic.

There remains, then, to consider the charge that humanized virus has undergone a serious loss of protective power-such loss as to make long-humanized virus unreliable, and to demand the substitution of bovine virus therefor. This charge has recently been formulated in the following series of propositions,* based upon the experience in England, more especially:

I. That the protection against small-pox afforded by the vaccine lymph in use, though still great, has become much less than it was when the lymph had undergone comparatively but few transmissions through the human subject.

II. That the number of cases of small-pox occurring per million of vaccinated persons is very much greater than that shown in the records of vaccinated populations in the earlier part of the century.

* Cameron, in the Fortnightly Review, May, 1881.

III. That the death-rate in recorded cases of post-vaccinal smallpox has progressively increased in all cases, with and without marks, from 1.75 per cent. in 1819-35, to over 10 per cent. in 1870-79, and in cases with marks from 6.9 per cent. in 1831-51 to 9.2 per cent. in 1870-79.

IV. That this increase in mortality has been remarkable in the best vaccinated classes of cases, the death-rate in cases with three or more cicatrices in 1870-79 being twice what it was in 1852-67 ; and the death-rate in cases with three or more good cicatrices in 1870-79 being thrice what it was in 1852–67.

V. That the proportion in which vaccinated children are attacked and cut off by small-pox has alarmingly increased, being many times greater during the last decade than it was thirty or forty years. earlier; and

VI. That while the death rate in small-pox occurring in unvaccinated persons has risen in the different groups recorded, and was exceptionally high in 1870-1879, the progressive advance of mortality in post-vaccinal small-pox is not to be attributable to epidemic influence, being equally observed in successive groups of cases in which the mortality from natural small-pox shows a diminution.

Every one of the counts in this indictment may be admitted; they are paralleled elsewhere in these pages in all essential features. But that these results are due to the use of long-humanized virus, per se, is not substantiated. If humanized virus remained unimpaired by its successive transmissions during the first twenty-five years of its use-and this is conceded even by the most interested of the advocates of bovine virus-there must be some reason for its subsequent impairment without assuming a change in character caused by its normal transmission through other human systems after Jenner's death. Jenner, himself, pointed out this reason. Everywhere throughout his writings he lays stress upon the proper performance of the operation; upon the importance of a perfect development of the vaccine vesicle, and of the undisturbed and normal progress of every stage of the vaccinal phenomena. Short of this he pronounced no vaccination to be fully protective. Still less did he countenance the use of lymph from such a non-protective vaccination, with the vain hope of securing full protection of others by it. He went further than do the advocates of the deterioration theory. They only assume that vaccine virus gradually loses its power of protecting against small-pox by successive transmissions through the human system. He asserted, after twenty years of characteristic painstaking investigation and record of facts, that the virus may undergo a change that will render it unfit for further use by passing even from one individual to another; and he pointed out the causes which might produce such change, and the indications by which such change might be recognized. Vaccine lymph from a perfect eighth-day vesicle-produced upon the arm of a healthy subject by lymph transmitted from arm to arm continuously since the original operation by Jenner himself-will to-day produce, in another healthy subject, the same vaccinal phenomena, identical in every respect of time, of appearance, duration and disappearance, and resulting cicatrix, as those produced in 1798 by Edward Jenner in England, or

in 1800, by Benjamin Waterhouse in the United States; and will confer as great a degree of protection, in this eighty-sixth year of vaccination, as did the original operations.

Increasing frequency of small-pox, within the last thirty years. among vaccinated persons, and the greater death-rate of post-vaccinal small-pox in the same period, are not to be ascribed to any loss of protective power in humanized virus; but rather to the causes elsewhere pointed out-to ignorance and want of care in the performance of the vaccinal operation; to absence of intelligent supervision over the progress of the vaccinal phenomena; to the use of virus from defective or non-protective vaccinations; and to the neglect of revaccination at the proper intervals.

To sum up, briefly, the foregoing considerations, on the choice of virus: Bovine virus has to recommend it-(1), convenience and certainty of supply; (2), popular favor on account of its freedom from danger of transmitting other diseases peculiar to mankind. Humanized virus has (1) promptness and uniformity of action; (2), mild, local and constitutional symptoms; (3) facility of propagation by every physician for himself, whereby he may be assured of the character of the material he is using.

PRACTICAL CONCLUSIONS AND PROPOSITIONS.

In the foregoing pages-The Small-Pox Epidemic of 1880-82; Vaccination in Illinois; and The Relations of Small-Pox and Vaccination -it is believed that the foundation has been laid for the following propositions and conclusions, based upon practical experience and supported by the concurrent testimony of a large number of competent observers. These are offered as an epitome of the subject, for the consideration of legislators; of municipal, sanitary and other authorities; of individual members of the community-parents, guardians, employers and others; and of the medical professioneach and every one of which classes owes a duty to the public welfare in this connection.

It has been demonstrated

I. That Small-Pox has increased in frequency of outbreak in Illinois, and in the extent of territory invaded in each successive outbreak, during the past thirty years; and that such outbreaks are costly in human life and suffering, as well as from a merely material standpoint.

II, That such increased frequency has kept pace with (a) the natural growth of population; (b) the increase of population by immigrants; and (c) the multiplication of means and facilities of communication. By the first and second of these factors, (a) and (b), the number of unprotected individuals, i. e., those susceptible to the small-pox contagion, accumulates from time to time up to the point when the introduction of the contagion from without is sufficient to cause an epidemic outbreak. By the second and third of these factors, (b) and (c), the contagion is introduced and disseminated, whenever the disease becomes prevalent in countries or places with which this country has commercial relations, and especially when, during such prevalence, foreign immigration rises above the average.