rRINOIPLES OF VETERINARY SURGERY 



165 



organisms than against their toxins. Antitoxic immunity 

 Metchnikoff presents as far more difficult of solution than 

 is that of acquired immtmity against micro-organisms. He 

 says that it is impossible to look to the body fluids for a 

 satisfactory explanation, but claims an interceptive power 

 on the part of the cells of the organs less vital than those 

 which the organisms aim to attack. In an animal immune 

 to tetanus for example, the liver cells may fix the toxin be- 

 fore it reaches the nervous centres, and prevent it from 

 doing harm. 



EHRLICH'S THEORY— SIDE-CHAIN THEORY.— 

 The author of this theory. Dr. Paul Ehrlich, A. M., the 



RECEPTORS 





H-C C-H 



PROTOPLASM 



Fig. 18a. 



director of the Royal Institute for Experimental Medicine 

 in Frankfort, first announced his brilliant discovery in 1885. 

 He is not only the author of the most probable theory of 

 immunity, but he is the most distinguished living hjemato- 

 logist and the author of our method of standardization of 

 antitoxin. 



Side-Chain Theory. — According to Ehrlich, every cell 

 of the body contains, besides its nucleus, a number of side- 

 chains, or receptors, arranged around it much the same as 

 the atoms in the benzene ring, in which six atoms of hy- 



