208 ORIGIN AND NATURE OF LIFE 



which confer the more or less perfect after- 

 immunity from any second attack of the 

 disease. As a rule, the more acute and 

 poisonous a disease product the greater the 

 after-immunity. 



On this knowledge is based both the 

 anti-toxic and vaccine treatments of disease 

 so successful in modern days, as well as 

 many of the new methods for the bacterio- 

 logical diagnosis of disease forms. 



In the antitoxic treatment of disease, 

 so conspicuously successful in diphtheria, 

 a vicarious animal is called in, one being 

 chosen which is itself susceptible to the 

 organism, but at the same time possesses a 

 fairly high resisting power. Such an animal 

 in the case of diphtheria is found in the 

 horse. Next the organism of the disease 

 is cultivated on a fairly large scale in a 

 nutrient broth or fluid culture medium. 

 After some days, the organisms are separated 

 by filtration through a fine filter such as a 

 Chamberland or Berkefeld candle, so yielding 

 a fluid in which the toxins of the disease are 

 dissolved. This filtrate is then injected in 

 graduated doses into the vicarious animal. 

 The cells of this animal set up a reaction, 

 destroy the poison, and manufacture, in ex- 

 cess, anti-toxins. The process is continued 



