730 INFECTION AND IMMUNITY. 



the same patient. Both presented vesicles on the 

 seventh day, the lymph of which I sent to London 

 to be used by Dr. Cory, the director of the Animal 

 Vaccine Institute of London. This calf lymph, 

 which Dr. Cory passed through a second calf before 

 using it on children, was the starting point of a 

 new vaccine at the institute. Between Nov. 21, 

 1885, and May 6, 1886, 1,247 children had been 

 vaccinated with this lymph and gave 98.4 per 

 cent, insertions of success." 



Concerning the changes which smallpox virus 

 undergoes in the cow, as a result of which it loses 

 permanently the power of causing smallpox in 

 man, we have no knowledge, aside from the hy- 

 pothesis of Councilman and others mentioned below. 



Etiology. We may pass over the various bacilli and cocci 

 which have been described as causing vaccinia and 

 smallpox with the remark that none of them are 

 of primary significance, but that they have been 

 either accidental contaminations or the causes of 

 secondary infections during the course of the dis- 

 ease. 



Theories. There are two chief theories as to the cause of 

 smallpox (and vaccinia) to-day. One, that the virus 

 is an ultra-microscopic and uncultivatable organ- 

 ism ; and a second, that it is represented by certain 

 protozoon-like bodies seen in the specific lesions 

 (vesicles, pustules) of both vaccinia and smallpox. 

 Concerning the first theory we know nothing be- 

 yond the observation of Parke that the virus of both 

 vaccinia and variola did not pass through Berke- 

 feld and Chamberland filters under the conditions 

 of his experiments. Of the second theory a brief 

 review may be given. 



