80 COLLECTED STUDIES IX IMMUNITY. 



of immunity. They seem to play an important role in the normal 

 processes of cell nutrition. As a result of experiments already 

 described we must assume that in the blood serum of a particular 

 animal species not merely a single complement exists but a large 

 number of different complements. It is understood, of course, that 

 not all the complements occurring in a large number of species differ 

 from one another. On the contrary it is to be regarded as certain 

 that particular types find a wide distribution extending over several 

 animal species. This explains why, for example, a hsemolytic or 

 bacteriolytic immune body can be reactivated by the sera of 

 different animal species. 



We have previously explained that a complement is to be con- 

 ceived as possessing two characteristic groups, a haptophore group 

 which fits into the complementophile group of the immune body, 

 and a zymotoxic group which is the actual carrier of the specific 

 action. A complement therefore, to a certain extent, corresponds to 

 a toxin, which possesses a haptophore and a toxophore group. Hence 

 by the immunization of suitable animals it is easy to obtain anti- 

 complements whose behavior corresponds exactly to that of anti- 

 toxins. For example, if a goat or rabbit is injected with horse 

 serum, an anticomplement will be formed which is able to specifically 

 inhibit the action of the complement contained in horse serum. We 

 have already shown l that this is due to a deflection of the comple- 

 ment. 



We have now tried to follow this analogy (between complements 

 and toxins) further. We take it for granted that it is generally 

 known that toxins, either through spontaneous changes or through 

 the action of chemical agents, become modified into toxoids, whose 

 distinguishing character is that they no longer possess a toxophore 

 group although the haptophore group remains. These toxoids, then, 

 are relatively non-toxic substances which are nevertheless able to 

 cause the formation of antitoxins in the animal body. Now we 

 know that the zymotoxic group is extremely sensitive to the most 

 varied influences; hence the attempt to study modifications of the 

 complements analogous to the toxoids seemed to promise favorable 

 results. Such modified complements would then be designated 

 complementoids. The first step was to see whether the well-known 

 inactivation of a serum by heating to 56 C. completely destroyed 



1 See Fourth Communication, page 56. 



