THE PROTECTIVE SUBSTANCES OF THE BLOOD. 383 



contained only a single complement, the course of the five series of 

 tests should have been identical when the complement was affected. 

 It was found on the contrary that under the influence of digestion, 

 for example, one completion remained intact, while four others dis- 

 appeared. By means of absorption further analogous differences 

 were manifested which made the assumption certain that in this case 

 four different complements come into action. Since these results 

 positively prove the existence of a plurality of complements I think 

 it will be unnecessary here to bring forward additional evidence in 

 support of this. 



A resume of these observations confirms my view that the mech- 

 anism of haemolysis and bacteriolysis is most easily explained by 

 the amboceptor theory. 



So far as the orgin of the two components which take part in 

 this reaction are concerned there is not the least doubt that they 

 are of cellular origin. 



I assume that, in addition to the ordinary receptors which serve 

 to take up relatively simple substances, the cells contain higher 

 kinds of receptors designed to take up large-moleculed albuminous 

 substances, as, for example, the contents of living cells. In this 

 case, however, the fixation or anchoring of the molecule constitutes 

 only a prerequisite for the cell's nutrition. Such a giant molecule 

 in its natural state is useless for the nutrition of the cell and can 

 be utilized only after it has been broken down into smaller constit- 

 uents by fermentative processes. This will be accomplished most 

 readily if the grasping group of the protoplasm is also the carrier 

 of one or several fermentative groups which will immediately come 

 into close relation with the molecule to be assimilated. It seems 

 as though the economy of cell life finds it advantageous for the re- 

 quired fermentative groups to come into action only temporarily, 

 perhaps only in case of need. This purpose is effected most simply 

 if the grasping group possesses another haptophore group which can 

 anchor the ferment-like substances present in the serum, the comple- 

 ments. Hence such a receptor of the higher order possesses two hapto- 

 phore groups of which one anchors the foodstuff, while the other is 

 complementophile. It is obvious that when, as a result of immuniza- 

 tion, such receptors reach the blood, they will exhibit the properties 

 which we have found to belong to the receptor type. 



In regard to the second constituent, the complements, we shall 

 not err if we regard these as simple cell secretions, designed to serve 



