VACCINES AND SERA 267 



There exists among cattle a disease resembling small-pox, 

 and also due to an unknown microbe, the cow-pox^ which 

 attacks also those who milk infected cows. Those individuals 

 who have suffered from the pustules of cow-pox are immune to 

 small-pox. 



This idea, popular in origin, had long been current among 

 farmers and cattle-breeders in certain districts of England, 

 France, Holland, and Germany when Jenner took it up 

 and consecrated his life and his genius to publishing it 

 abroad. 



He made of the subject a definite experimental study : he 

 inoculated in turn the virus from animal to animal, from the 

 animal to man, from man to man, and finally submitted his 

 " vaccinated " subjects to experimental inoculation with small- 

 pox. 



In all countries where public health is well organized vacci- 

 nation has been made compulsory ; in consequence smallpox 

 has almost disappeared from Germany : the rare cases recorded 

 there are cases of immigrants or inhabitants on the frontiers. 

 It has very much diminished in France and is being actively 

 combated in the French colonies. It may one day become 

 extinct. 



Three improvements have been introduced in Jennerian 

 vaccination since Jenner's time. In the first place, it was 

 recognized that in many cases vaccination does not protect for 

 the whole of life, and periodical revaccinations have become 

 customary and even in certain countries compulsory. In the 

 second place, instead of vaccinating from man to man the 

 vaccine employed is derived from animals. Jenner practised 

 " arm to arm " vaccination, i.e., transmitted from man to 

 man a virus whose distant origin was cowpox. This practice 

 had the inconvenience of occasionally transmitting human 

 diseases such as syphilis. From 1860 onwards vaccination in 

 Europe has been performed with " animal lymph " taken 

 from vaccine calves (in certain colonies from buffalos, rabbits, 

 zebras, &c.). 



Finally we have learned to preserve and purify the supply of 



