52 IMMUNE SERA. 



that of the possibility to artificially increase them. 

 A number of authors, among them Nolf and Muller, 

 have answered this question in the affirmative. 

 They believe they have noticed such an increase 

 following the injection of an animal with all sorts 

 cf substances, such as normal serum of another 

 animal, sterile bouillon, etc. v. Dungern, as well 

 as myself and others, have not been able to convince 

 ourselves of the possibility of such a definite in- 

 crease. I tried to excite the increased production 

 of complement by injecting guinea-pigs for some 

 time with anti-complement. This being the oppo- 

 site of the complement, I hoped to be able by im- 

 munizing to excite an increase of the complements. 

 In this I was unsuccessful, though of course it may 

 be 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, 

 anti -toxins, ferments, anti-ferments, 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 



