INFECTION AND IMMUNITY. 603 



garded as non-irritating and harmless. For instance, 

 we have learned that the blood of one animal may cause 

 fatal intoxication when injected into an animal of dif- 

 ferent species; but if that blood be repeatedly injected 

 in non-fatal amounts, the animal receiving 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 dissolving its 

 corpuscles (ha?molysis) in a test-tube. In an analogous 

 way, if such tissue-cells as epithelium or spermatozoa 

 be injected repeatedly into the tissues of animals, the 

 serum of the blood of those animals acquires the power 

 of 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 L e., precipitates it. From the foregoing 

 we see that in the numerous phases and expressions of 

 this physiological possibility there are produced anti- 

 bodies having functions totally different from those 

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

 lysins, agglutinins, precipitins, 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 neu- 

 tralization of a bacterial toxin by an antitoxin; and, 

 what is more to the point, in many of these conditions 

 Gi immunity or tolerance above noted antitoxins as we 

 know them, are not present at all. 



In an important series of papers on the ha3molysins 

 published by Ehrlich and Morgenroth 1 an effort is 



1 Ehrlich und Morgenroth : Berliner klinische Wochenschrift, 1899, 



