SMALLPOX AND VACCINATION. 507 



for believing that it consists in an active immunisation by means of an 

 attenuated form of the causal organism. As to how immunity is main- 

 tained after vaccination, we do not know much. Some, including 

 B6clere, Chambon, and M6nard (who jointly investigated the subject), 

 maintain that in the blood of vaccinated animals substances exist which, 

 when transferred to other animals, can confer a certain degree of passive 

 immunity against vaccination, and which have also a degree of curative 

 action in animals already vaccinated. Beumer and Peiper, on the other 

 hand, could not find evidence of the existence of such bodies. If they 

 do exist, we cannot as yet say whether they are antitoxic or antimicrobic. 



