336 COLLECTED STUDIES IN IMMUNITY. 



important to determine whether the hsemolytic agent is a haptin 

 in the true sense. So far as the alkaloids, glucosides, etc., which 

 act hsemolytically are concerned, they are generally readily identi- 

 fied by means of the chemical methods devised for their separation, 

 methods based on precipitations and shaking out with solvents. 

 This is not true for the haptins; they cannot be prepared by these 

 methods. At the most, it is possible to precipitate them in con- 

 junction with the albuminous bodies. Another distinction consists 

 in this, that the substances which are chemically defined are usu- 

 ally thermostable, while the haptins in the great majority of cases 

 are destroyed by heat, especially by boiling temperature. One 

 distinction above all, however, is the fact that only the haptins are 

 capable of causing the production of antibodies by immunization, 

 .and this makes a classification possible even in difficult cases. Fre- 

 quently the facts which we have already learned about a substance 

 allow us to make definite conjectures. For example, if a vegetable 

 extract possesses hsemolytic properties which are not destroyed by 

 boiling, and if it is found that the hsemolytic substance is soluble 

 in ether, we can at once exclude this from the class of haptins. On 

 the other hand, if one finds that the hsemolytic action of an animal 

 body fluid is destroyed by heating to 56 C., this fact already argues 

 in favor of a haptin; Other methods, including perhaps the immu- 

 nizing reaction, would then be required to determine this positively. 



V. The Study of Complex Haemolysins. 



We now take up a question of paramount importance which 

 arises in the study of every hsemolytic poison, namely, whether in 

 any given instance we are dealing with a simple hsemolysin, or with a 

 complex one consisting of amboceptor and complement. 



In determining the complex nature of a hsemolysin we now have 

 the following methods at our disposal: 



1. Separation of amboceptor and complement by allowing the 

 former to be tied by red blood-cells at low temperatures. 



2. Removal of the complement or changing the same into the 

 inert complementoid. 



(a) Absorbing the complement by means of certain cells (e.g., 

 yeast-cells, bacterial cells, cells of animal organs), or by means of 

 porous filters. 



