296 LECTURES ON IMMUNITY 



cipitin against sheep-serum, 212 equivalents of precipitin 

 against goat-serum, and only 90 equivalents of pre- 

 cipitin against bullock-serum. All of these three normal 

 sera contain 2000 equivalents per centimeter cube. In 

 the same manner and in nearly the same proportion 

 the constant of reaction sinks from 250 for sheep-serum 

 to about 170 for goat- and to 85 for bullock-serum. 

 Probably the sheep-serum contains additional substances 

 which occur also in sera of goats and of bullocks, which 

 after injection into rabbits produce antibodies against 

 these sera, although in lesser proportions than the pre- 

 cipitin against the chief substance in sheep-serum, which 

 gives a precipitate with the serum from the inoculated 

 rabbit. The observations lead to the conclusion that 

 we have a mixture of three different precipitins in the 

 rabbit-serum. Otherwise it is difficult to understand that 

 i c.c. of all the three normal sera, from sheep, goat, 

 and bullock, contain nearly the same number (2000) of 

 equivalents of the precipitate formed. As 100 equivalents 

 pack a volume of 0.04 c.c., the precipitates given by i c.c. 

 of the rabbit-serum would pack a volume of 0.24 c.c., 

 of which probably only a small part is derived from this 

 serum itself, the chief part being derived from the other 

 sera. 



The experiments with precipitins lead to the conclusion 

 that they are really bound in the precipitates and do not 

 act as catalytic agents. The action of agglutinins dis- 

 plays a very great similarity to that of the precipitins, so 

 that it is reasonable also for this case to assume a real 

 chemical reaction in stoichiometric proportions and not a 

 catalytic action. Further, we have observed that haemo- 



