THE DEFENSES OF THE BODY 281 



of Wright upon his opsonic doctrine has finally placed the 

 leukocyte among the important defenses of the body and 

 the profoundly interesting investigations of Bordet, Moxter, 

 von Dungern, Fish, and others, have shown that immunity 

 reactions may be induced with cells and secretions of animal 

 origin hitherto regarded as non-irritating and harmless. For 

 instance, we have long known that the blood of one animal 

 may cause fatal intoxication when injected into an animal 

 of different species; but later we learned if that blood be 

 repeatedly injected in non-fatal amounts, the animal receiv- 

 ing the injections after a while becomes tolerant, and its 

 serum reveals the property not only of robbing the alien 

 blood of its hurtful properties, but also of actually dissolv- 

 ing its corpuscles in a test-tube (hemolysis). In an analogous 

 way, if such tissue-cells as epithelium or spermatozoa be in- 

 jected repeatedly into the tissues of animals, the serum of 

 the blood of those animals acquires the power of agglutinat- 

 ing and finally dissolving (digesting) such cells outside the 

 body; and if so inert a secretion as milk be injected into 

 the tissues, the blood-serum of the animal receiving the 

 injections after a time reacts specifically with that milk in 

 a test-tube — i. e., precipitates it. 



From the foregoing we see that in the numerous phases 

 and expressions of this physiological possibility there are 

 produced antibodies having functions totally different from 

 those attributed by Ehrlich to antitoxins — i. e., we have 

 "lysins," "agglutinins," "precipitins," "aggressins," "op- 

 sonins," etc., that in their mode of action suggest ferments 

 with specific affinities. It is evident that when broadly 

 conceived the mechanism of immunity comprehends very 

 much more than the neutralization of a bacterial toxin 

 by an antitoxin; and, what is more to the point, in many 



