674 SA CTERtOL OOY. 



bacteria is regarded by many as a concomitant of infec- 

 tion, the exhibition of this property by the blood of 

 immune animals may at first sight appear paradoxical. 

 We should not lose sight of the fact, however, that 

 agglutinin is presumably distinct from the other sub- 

 stances concerned in immunity, and its presence in im- 

 mune animals may, therefore, be reasonably explained 

 as a more or less permanent result of the " reactions of 

 infection " that were coincident with the primary stimu- 

 lations by specific infective or intoxicating matters nec- 

 essary to the establishment of the condition of immunity ; 

 nor shonld we in this connection lose sight of the fact 

 that its presence is constantly to be demonstrated in 

 typical cases of typhoid fever, for instance, that termi- 

 nate fatally, and that have exhibited little or no clinical 

 signs of resistance at any time during their course. 

 Fifth, there may be demonstrated in the blood of ani- 

 mals that have received repeated subcutaneous injections 

 of milk a body — a " precipitin " — that causes a precipi- 

 tation of milk. This precipitation represents apparently 

 a specific reaction, for it occurs only when the blood- 

 serum is mixed with milk from the species of animal 

 that supplied the milk used for the injections. Sixth, 

 after the repeated injection of blood or of emulsions of 

 tissue-cells into the body of an animal, there appear in 

 the blood of that animal certain solvents, or enzyme-like 

 bodies, " hsemolysins," " cytolysins," etc., that react 

 specifically upon the blood or tissue-cells injected ; 

 agglutinating, disintegrating, and finally completely 

 dissolving them. Here, too, the relations are specific. 

 If a rabbit, for instance, be rendered tolerant to or 

 immune from beef-blood, its serum dissolves only the 

 red corpuscles of bovines ; if from dog's blood, then 



