CONTRIBUTIONS TO THE STUDY OF IMMUNITY. 39 



complement, for equal amounts of immune body act differently with 

 different amounts of complement. In all my tests on the amount of 

 complement contained in a serum, I used so much inactivated blood 

 immune serum that the immune body, when saturated with com- 

 plement, could dissolve sixteen times the amount of blood present. 



The experiments demonstrated that the amount of complement 

 contained in normal rabbit serum is fairly constant, and even in 

 different animals is not subject to great fluctuations. Proceeding 

 as just described, it was found that complete solution took place 

 in all cases on the addition of 1 / 4 o to 1 / 2 o cc. normal serum. Within 

 definite limits therefore the complement hi rabbit blood seems fixed. 



The amount of complement contained in immune serum could be 

 determined by comparing the haemolytic action of the fresh serum 

 with its action, after inactivation (by heating for twenty minutes 

 to 56 C.). on the addition of various amounts of normal rabbit serum, 

 the complement content of which was known. 



The serum of the rabbits treated with cattle blood, serum which had 

 been shown to contain such a large excess of immune body, was tested 

 1 } 2, 8, 4, 11, and 14 days after the injection and failed in all of the 

 numerous cases to show even a trace of increase in the amount of com- 

 plement it contained. A peculiar state of affairs is thus presented. 

 Since haemolytic action is dependent on the immune body so far 

 as this can combine with the complement, we see that the haemolytic 

 action of fresh immune serum can be increased only up to a certain 

 point, determined by the amount of complement contained in the 

 normal blood serum. All additional amounts of immune body 

 formed hi the course of the immunity reaction therefore remain 

 latent, and manifest their action only when the immune body is 

 brought into combination with greater amounts of complement. 

 This can be done artificially, in test tube experiments, by the addi- 

 tion of normal serum, or experimentally by injecting the immune 

 body into a suitable animal body. 1 



Immune serum therefore differs from normal serum only in its con- 

 tent of inactive immune body. Accordingly, in the immunity reaction, 

 only inactive immune body is produced by the cells in excess. This 



1 So also the earlier observations, as those of R. Pfeiffer, on cholera serum, 

 my own on epithelial immune serum, and those of Moxter on antispermatozoa 

 serum, in which the immune sera, in themselves little or not at all active, showed 

 their full power when injected into fitting animal bodies, are to be explained 

 by the relative poverty of these sera in preformed complement. 



