238 



COLLECTED STUDIES IN IMMUNITY. 



Hence within three days the serum of the horse has become 

 strongly hsemolytic for guinea-pig blood without altering its haemo- 

 lytic property for rabbit blood, whereas within a further three weeks 

 its properties have almost become reversed, since now it does not 

 dissolve guinea-pig blood at all, and dissolves rabbit blood (which 

 at first was but slightly affected) very strongly. It is worthy of 

 note that in almost every horse serum which we examined for the 

 purpose we found a considerable amount of amboceptor for guinea- 

 pig blood. This amboceptor was characterized by a particularly 

 high degree of thermolability, being invariably destroyed by heat- 

 ing to 55 C. A complement for the same is very often absent, and 

 even when present it is only on the addition of considerable amounts 

 of fresh guinea-pig serum that this amboceptor becomes manifest. 



The cause of this varying haBmolytic property of the horse serum, 

 which is in contrast to the extraordinarily constant amount of normal 

 hsemolysin present in other sera, e.g. goat serum and dog serum, is 

 perhaps due in part to the unusual lability of the complements here 

 concerned. We often observed that a horse serum which dissolved 

 guinea-pig or rabbit blood completely lost this property, or nearly 

 so, by keeping the serum on ice for twenty-four hours, a behavior 

 which we never met with in other sera. 



In a similar manner horse serum shows its variability when it is 

 employed purely as a source of complement. We have frequently 

 used horse serum as complement in the following combinations: 



Of all these cases only the complement for 6 and for 8 w r as present 

 in considerable amounts. 80 far as the other six complements were 

 concerned we observed a fundamental difference between the ex- 

 periments which we had made some years ago in Steglitz and those 

 made during the past two years in Frankfurt. Whereas formerly 



