168 STUDIES IN IMMUNITY. 



afforded by injecting antibacterial sera. We know that cholera 

 serum when injected into a normal animal causes a remarkable 

 phenomenon : the serum of the treated animal becomes bactericidal 

 for the cholera vibrio.* It is important to determine whether the 

 serum from a rabbit injected with a serum active against hen cor- 

 puscles becomes destructive for these corpuscles. 



A small amount of blood is taken from a normal rabbit and gives 

 serum A. After bleeding, the rabbit is given 10 c.c. of active serum 

 subcutaneously. On the following day the animal is bled again 

 and serum B is obtained from this bleeding. The hemolytic proper- 

 ties of serum A may be compared with those of serum B. It is 

 found that serum B has a distinct hemolytic property for hen cor- 

 puscles, whereas serum A, from the normal rabbit, has only the 

 faintest activity. Serum B also has an agglutinating property, 

 which, however, is slight. This property has been transmitted, 

 although much weakened by dilution in the fluids of the normal 

 rabbit. It is found, indeed, that although the active serum em- 

 ployed agglutinates three or four volumes of hen blood if diluted 

 with 20 to 25 parts of normal salt solution it causes no rapid agglu- 

 tination in any dose.f We have already noted the fact that agglu- 

 tinins when injected subcutaneously into a normal animal go into 

 the blood rapidly.J 



The most natural conclusion to be drawn from this experiment 

 is that the active substances in serum, when injected subcutaneously, 

 are simply diluted in the fluids of the recipient. It follows, there- 

 fore, that the serum of this latter animal should acquire to a less 

 degree all the properties which characterize the active serum in- 

 jected. And this, in fact, is what happens. When heated to 55 

 degrees, serum B loses its destructive property, but recovers it on the 

 addition of a little of serum A (normal serum). It is scarcely 

 necessary to note that experiments such as these are controlled 



* This important fact was noted for the first time by Fraenkel and Sobernheim, 

 Hygienische Rundschau, 1894, No. 1. 



t Under these conditions the agglutination occurs only after a considerable 

 period. The same is true of serum B. When agglutination is very slow heated 

 sera must be used. 



I See article, page 56. Agglutinins injected under the skin are also found in 

 the peritoneal exudate, but in smaller amounts than in the blood. (The experi- 

 ment to demonstrate this fact was done with cholera serum.) 



