ANTITOXINS 85 



an understanding of the most advanced views regard- 

 ing them, as expounded by Ehrlich and others Ehr- 

 lich's "side chain theory." In a popular treatise a 

 simple statement of well ascertained facts will, I hope, 

 be appreciated, while an exposition of theories still 

 under discussion might prove wearisome. 



It has been shown that the antitoxins when mixed 

 with toxins in a test-tube exhibit their specific neutral- 

 ising action as shown by the innocuousness of the 

 mixture when injected beneath the skin of a sus- 

 ceptible animal. 



The antitoxin of snake poison, which has been suc- 

 cessfully used in India for the cure of persons bitten 

 by the deadly cobra, when mixed with cobra venom 

 in proper proportion completely neutralises the poi- 

 sonous properties of this venom. Such a mixture 

 injected beneath the skin of a small animal is without 

 effect. But if the mixture is heated to 70 C. the 

 antitoxin is destroyed and by inoculation experiments 

 the toxin is found to be still present and active. 



The facts stated show that in certain infectious 

 diseases acquired immunity depends upon the forma- 

 tion of antitoxins in the bodies of immune animals. 

 But these antitoxins have no power to destroy 

 specific disease germs. They neutralise the toxic 

 products of these germs without exhibiting any 

 germicidal action upon the germs themselves. As, 



