cause of uncertainty arises from the fact that this "variolous test" consisted in inoculating with small-pox virus obtained from the last of a series of successive patients in whom the effect produced was a minimum, consisting of very few pustules, sometimes only one, and a very slight amount of fever. The results of this test, whether on a person who had had cow-pox or who had not had it, was usually so slight that it could easily be described by a believer in the influence of the one disease on the other as having "no effect"; and Dr. Creighton declares, after a study of the whole literature of the subject, that the description of the results of the test is almost always loose and general, and that in the few cases where more detail is given the symptoms described are almost the same in the vaccinated as in the unvaccinated. Again, no careful tests were ever made by inoculating at the same time, and in exactly the same way, two groups of persons of similar age, constitution, and health, the one group having been vaccinated the other not, and none of them having had small-pox, and then having the resulting effects carefully described and compared by independent experts. Such "control" experiments would now be required in any case of such importance as this; but it was never done in the early days of vaccination, and it appears never to have been done to this day. The alleged "test" was, it is true, applied in a great number of cases by the early observers, especially by Dr. "Woodville, physician to a small-pox hospital; but Dr. Creighton shows reason for believing that the lymph he used was contaminated with small-
those who applied the so-called "variolous test" in the early days of vaccination paid any attention to this long list of ailments, many of which were very prevalent at the time, and which would, in the opinion of De Haën, and of the English writer Sanders, who quotes him, have prevented the action of the virus and thus rendered the "test" entirely fallacious. With such causes as these, added to those already discussed, it becomes less difficult to understand how it was that the alleged test was thought to prove the influence of the previous vaccination without really doing so.
