92 IMMUNE SERA 



all sorts of substances, such as normal serum of 

 another animal, sterile bouillon, etc. v. Dungern, 

 Wassermann and others, have not been able to con- 

 vince themselves of the possibility of such a definite 

 increase. Wassermann tried to excite the increased 

 production of complement by injecting guinea pigs 

 for some time with anticomplement. This being 

 the opposite of the complement, he hoped to be 

 able by immunizing to excite an increase of the 

 complements. In this he was unsuccessful, though 

 of course it maybe possible with another species of 

 animal. 



Despite all this, we must believe that the amount 

 of complement, as well as the amount of other active 

 substances of the blood, inter-bodies, agglutinins, 

 antitoxins, ferments, antiferments, etc., is subject 

 to great fluctuations even in the same individual, 

 a constant change going on within the organism. 

 Ehrlich, in particular, has pointed out these indi- 

 vidual and periodic variations and has insisted on 

 their importance. Very likely, under circumstances 

 of which we now know very little, these substances 

 are at certain times produced in greater amounts, 

 at other times in lesser; sometimes they may be 

 absent entirely in an individual in whom they were 

 previously present. For example, the serum of a 

 dog will at times dissolve the red cells of cats, rab- 

 bits, and guinea pigs, at other times not. Further- 

 more, the serum of one and the same animal may 



