The history of vaccination and its adoption as a prophylactic measure are too well known to need repeating here. The evolution of the vaccine virus is, however, another matter, on which a striking lack of information seems to exist among some of the most practical members of the profession, and I feel that in addressing you upon this subject I may arrange the matter in a new and suggestive form for your subsequent reflection if I contribute no new facts to your store of knowledge.
1. The Relation of Vaccinia to Variola.
—This has been the subject of arguments from the very inception of Jenner's theory that cowpox protected against smallpox, and there is still some lack of uniformity in the opinions of different writers. Without entering into details, the relationship stands somewhat as follows:A century ago, when everybody expected at some period of his life to have smallpox,
McFARLAND J. VACCINE VIRUS—ITS PREPARATION AND THE COMPLICATIONS ATTENDING ITS USE.. JAMA. 1902;XXXVIII(4):217–220. doi:10.1001/jama.1902.62480040003001a
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