It was early observed that a person who had once had small-pox was not very liable to suffer from it a second time. Ex periments made in China and India at a very early period showed that when the disease was induced by inoculation it was much less severe than when contracted in the usual way. This led to the employment in those countries of inoculation as a means of prevention of the disease. The same practice was introduced into Europe. It never became popular, however, from the fact that death not infrequently occurred in consequence of inoculation, and it was found that the disease was as violent when communicated by those suffering from the effects of inoculation as when acquired in the usual way.

In the eighteenth century, the supposed discovery was made in various parts of the world that a disease known as cow-pox was identical with small-pox in human beings. According to Humboldt, this was known to the mountaineers of Mexico for many years before the time of Jenner. In Gloucestershire, England, there was a traditional belief that persons who had acquired cow-pox by milking cows affected with the disease were thereby protected from small-pox. This belief led Jenner to experiment with the virus of cow-pox, and his experiments resulted in the invention of vaccination as a means of protection from small-pox.

The peculiarity of small-pox in lower animals is that its manifestation is chiefly local. In the cow, the pocks or pustules occur almost exclusively upon the udder and teats. In horses the disease is confined to the foot-joints. Sheep, goats, pigs, asses, dogs and monkeys are also subject to this disease.

The evidence is very strong that the so-called small-pox of animals is really the same disease as affects human beings, but the eminent authority quoted freely admits that the facts relied upon "do not absolutely prove it." Experience does seem to show, however, that inoculation with the virus of cow-pox, or with that obtained from the same disease in other animals, will produce a disease supposed to be modified small-pox, which will to some extent exercise the same preventive influence as the real disease itself. On this point the author before mentioned says:"In spite of the efforts of its opponents, no unprejudiced person at the present day can any longer be in doubt as to the efficacy and eminent practical value of vaccination. In countries where it has been introduced, and in a measure systematically carried out, the number, the intensity, and the extent of small-pox epidemics have been notably diminished, and in a manner which of itself renders the idea of mere coincidence inadmissible. In this connection nothing could be more convincing than the exceedingly interesting and graphic account which Kussmaul gives of the mortality from variola, in Sweden, during a period of one hundred years, in the latter half of which vaccination was universally practiced. Moreover, for Germany, France, and England a somewhat similar decrease in the small-pox mortality might be demonstrated. If, notwithstanding all these proofs, we for the moment entertain the supposition, improbable as it is, that this decrease in the epidemics is a matter of mere accident, it at once falls to the ground as soon as we proceed further into detail. We see, first of all, that where vaccination is regularly practiced in very early life, the mortality of children from small-pox, instead of being as enormous as amongst those not vaccinated, is almost nil. We notice, further, that where the vaccination of adults, as for example in the Prussian army, is performed with regularity, epidemics of the disease no longer occur. With these facts before us, the idea of mere coincidence is out of the question. The trial of vaccination in the Prussian army has conclusively demonstrated the efficacy of the measure, to test which we have only to compare the relative immunity of soldiers during great epidemics of small-pox with the mortality in classes of the same general age in the civil community where vaccination is imperfectly carried out."

Dr. Alonzo Clarke, professor of the theory and practice of medicine in the College of Physicians and Surgeons in New York City, and one of the most eminent physicians of this country, in a lecture on small-pox reported in the Medical Record, remarked as follows:"Vaccination has been generally practiced in civilized nations for seventy years; it took it about ten years to acquire general favor, since which time almost everybody has been vaccinated And the history of the last seventy years gives us a longer duration of human life every succeeding ten years (a less number of deaths in proportion to the number living); and if everybody be vaccinated, and everybody's life be made shorter by vaccination, you observe that this is rather a singular commentary. Every ten years is marked as giving additional length to human life (diminishing the proportions of deaths every year to the number living). I know no other commentary that need be made in regard to it."

The above quotation presents a practical argument which those who oppose vaccination under any and all circumstances will find hard to meet unless they can show that the statement respecting the length of human life is incorrect.

It is admitted by all who are in any degree conversant with the subject that vaccination is not free from disadvantages and even dangers. Experience shows very clearly that it affords immunity only for a period of eight to twelve years. It is settled beyond question that it may be the means of communicating the worst and most loathsome diseases, when humanized lymph is employed, though this evil may be wholly avoided by the use of bovine virus, or that taken direct from a calf suffering with the disease. It appears to us that in all cases in which vaccination is employed, only the latter kind of virus should be used. We have never known of any injury arising from bovine virus, and think the evidence is very clear that small-pox may be prevented in this way by vaccination.

In some countries, vaccination is made compulsory by law. This has aroused a vigorous opposition on the part of those who are opposed to the practice, and at the present time efforts are being made, especially in England and Scotland, to secure a repeal of the compulsory laws. The anti-vaccinators are not wholly unsustained in their efforts, quite a number of eminent English physicians having taken a stand in opposition to the practice. Quite recently, a petition signed by several hundred physicians was presented to the English parliament, calling for the repeal of the obnoxious laws.

It is probable that the benefits of vaccination on the one hand, and on the other its evils, have been considerably exaggerated. It may be considered as thoroughly settled, however, that vaccination with human virus, that is, with scabs or matter taken from the sore produced in persons by vaccination, should be entirely discarded, and that bovine virus alone, if any, should be employed.