Possibly hardly any discovery has ever been made of so much benefit to the human race, as that Cow-Pox was a protection against the contagion of Small-Pox. When we consider that Small-Pox has always been, not only the most disgusting, but one of the most fatal of diseases; when we think of the thousands who in past ages used to die of this hideous disease, and of many who when recovered were disfigured for life, we can hardly express our gratitude to that individual, the late Dr. Jenner, whose persevering investigations led to so valuable a discovery.

At the time the discovery was made, inoculation for Small-Pox was largely practised in England, as it was found that those who were inoculated for the disease, when they were in a good state of health, had it more favourably than those who took it in a natural way, when, perhaps, the system was out of order. Dr. Jenner, being largely engaged in the practice of inoculation in the county of Gloucester, in England, found certain individuals who would not take the disease. On inquiry he ascertained that these parties had had a complaint from the Cows (caught by milking them when the teats were affected with pustules,) which complaint, in that neighborhood, was supposed to be a preventive against the Small-Pox. The idea occurred to Dr. Jenner that the complaint might be artificially communicated from one individual to another, and he immediately commenced a series of experiments to test the facts. Having collected sufficient proofs, he published in June, 1798, an essay, entitled, "Inquiry into the cause and effects of the Variola Vaccinae." This essay attracted great attention, additional evidence was soon accumulated; and the practice of Vaccination spread with great rapidity. The British Parliament voted Dr. Jenner the handsome sum of 30,000 sterling. "In 1799, Vaccination reached the United States; in the following year it was admitted into France, and other parts of Europe, and even to India, and very soon to almost all portions of the world."

Opinions differ as to the age at which to vaccinate a child. A good deal must, of course, depend upon the state of the child's health, as it is desirable that the child, when vaccinated, should, if possible, be in a good state of health. Then again, the sooner the child is vaccinated the less chance there is of its suffering from its coming in the way of Small-Pox. I have vaccinated persons of all ages, and I think the sooner a child is vaccinated after it is six months old the better. It is not generally supposed that any other disease can be communicated along with that complaint, but, as many people have a little prejudice on that point, it is as well to select a healthy child to vaccinate from, and vaccination is now so universal that there is usually no difficulty in finding one whose state of health is satisfactory. In vaccinating a child, I have generally inserted the lymph in one place in each arm; this is the usual English practice. In vaccinating, the less blood there is drawn from the puncture the better. I have little doubt that many of the cases of "failure" have arisen from the bleeding from the puncture washing out the lymph. In America, it is a common practice to take the scab from the child and use that for the purposes of vaccination; but in England the lymph is generally employed, either fresh or preserved on little pieces of ivory, called Points, or else between two pieces of glass, about an inch square. Where possible, the children, the one to supply the lymph, and the children to be vaccinated, are brought together. Two or three punctures are made in the vesicle with a lancet; the ivory points, or rather, the points of the ivory points are dipped in the oozing lymph, and allowed partially to dry for two or three minutes; then, a very slight puncture is made in the arm of the child to be vaccinated, and one of the points inserted in the puncture, and allowed to remain there for ten or fifteen minutes, after which it is withdrawn. Occasionally, after making the puncture, the lancet itself is dipped in the lymph, and then re-inserted in the puncture, and the lymph wiped as it were, into the wound. Sometimes the lymph is obtained by making small punctures in the sides of the vesicle, then gently pressing the glass thereon, the lymph oozing on to the glass. Another piece of glass is placed on the first, and the lymph glues the glasses together. When wanted for use, the glass is held over the steam from a cup of hot water, and the glasses soon separate. I once vaccinated forty (of all ages) one afternoon. Having previously vaccinated two or three children in the village where the others resided, I made an appointment for them all to meet me in the school-house on the ninth day, and, having a plentiful supply of points, the operation was soon over. Out of that forty only two required re-vaccination.

Vaccine-lymph is sometimes put up in small glass tubes for sending to a distance, but they are too liable to accidents. When practicing in Illinois, some years ago, I wrote to the Royal Vaccine institution, at London, (England), for some lymph, which was sent-me in a letter. There were two or three tubes, and two or three points. The tubes were smashed, I suppose, in stamping the letter; and I got just lymph sufficient to vaccinate one child; from that I vaccinated others, and eventually nearly all the children in the neighbourhood. Although the lymph on the points had been six weeks on the way it was perfectly good. The eighth or the ninth day is the usual time for taking the lymph in England. If taken on the eighth, the child vaccinated therewith will usually have the Cow-Pox at the height a little earlier than if taken on the ninth day.

The majority of children suffer so little from vaccination that no after treatment is necessary, beyond taking care to arrange the sleeves of the child's dress in such a way that they do not rub and irritate the pustules. About the third day after vaccination the pustule begins to rise, and continues enlarging till about the seventh or eighth day, when it is round, flattened at the top, of a pale pinkish or flesh-coloured tint, semi-transparent, and, in point of shape, very much resembling those seeds of the mallow tribe, called "cheeses" by the children. There is generally a little redness of the skin surrounding the pustule, which increases in diameter with the growth of the pustule. About the tenth day the pustule loses its transparency and becomes opaque, and, after a few more days, dries up, and the scab falls off.

It sometimes happens that about the fifth or sixth day the child becomes feverish, and restless; when this is the case, a few mild doses of Magnesia, or Magnesia and Rhubarb, or Castor Oil will be sufficient to effect a change.

Some persons are much less susceptible to the Vaccine virus than others, and more or less so at one time than another. I have known children vaccinated five or six times without taking the infection, although there was no doubt about the goodness of the lymph. On the other hand, I recollect an instance of a child four or five years old, which not only perfected the pustules on the arms, where the lymph was inserted, but, actually had a crop of pustules distributed over the body-some ten or twelve of them-which were perfect Vaccine pustules, and ripened about the same time as those on the arms. In this case the constitutional disturbance was not greater than that of the general average of patients. Some people have an idea that, after a certain number of years, the effect of the Vaccination wears off, and that, in order to insure protection against Small-Pox, it is necessary to re-vaccinate; but the experience of the majority of the medical profession does not encourage that idea. It is true that, occasionally, a person who has been vaccinated will take Small-Pox, but the disease is always mild, and it is certain that not a greater number of persons take Small-Pox after vaccination, than take Small-Pox a second time.

In case of the appearance of Small-Pox in any neighbourhood, the inhabitants should not hesitate a moment, but should there be any amongst them-young or old-who have not been vaccinated, they should have the operation performed at once; even when the Small-Pox has attacked one member of a family, the vaccinating the remainder (even if they are living in the same house), will usually prevent the spreading of the disease.

Some people have a prejudice against having their children vaccinated, from the idea that other diseases may be propagated from child to child along with the Cow-Pox; this, however, is quite a needless alarm, as the experience of the Profession leads them to quite a contrary opinion.