12 VACCINE AND SERUM THERAPY 



large number of different substances, chief among 

 which are the red blood cells. 



Bordet and others have shown that the serum of 

 animals repeatedly injected with defibrinated blood 

 of another species exhibited the specific power of 

 dissolving the red blood corpuscles of this species. 

 This phenomenon is known as hemolysis. Likewise, 

 by using spermatozoa in place of blood, a serum can 

 be produced which will seriously injure these highly 

 speciaUsed cells. To this latter substance the name of 

 " cytolysins " has been given. The formation of cyto- 

 lysins is not, however, general for all tissues of the 

 body. The stimulation of antibody formation in the 

 sera of animals is a consequence, therefore, of the 

 injection of a large variety of substances — some of 

 them poisonous, some quite innocuous. The sub- 

 stances possessing this power have been named 

 ** antigens." 



The Toxin : Antitoxin Reaction, — The problem 

 which now faces us is the manner in which toxin is 

 made innocuous by the action of antitoxin. Ehrlich 

 endeavoured to explain this phenomenon by conceiving 

 that the reaction of toxin and antitoxin was a direct 

 union, analogous to the chemical neutralisation of an 

 acid by a base. Soon, however, Calmette and Wasser- 

 mann, by experiments, were able to contradict this 

 idea. These workers showed that the toxin only 

 became inactivated by the presence of the antitoxin, 

 the toxin again becoming reactivated after the 

 destruction of the antitoxin by heat. 



