372 COLLECTED STUDIES IN IMMUNITY. 



These explanations will suffice to show that the term assimila- 

 bility, as I employ it, is restricted somewhat more than is customary, 

 for I reserve it exclusively for the specific nutritive substances of the 

 living protoplasm. According to this view the process of cell assimila- 

 tions is a synthetic one which presupposes the presence of two groups 

 effecting the synthesis and having a strong chemical affinity for each 

 other. 



Hence I assume that the living protoplasm possesses side-chains 

 or receptors which possess a maximum chemical affinity for certain 

 particular groups of the specific nutritive substances, and that they 

 therefore anchor these substances to the cell. The receptor apparatus 

 of the cells is highly complicated, the red blood-cell, for example, 

 possessing perhaps a hundred different types of receptors. 



If this view is accepted and it is recalled that in the toxin mole- 

 cule it is the haptophore group which effects the development of 

 immunity, only a very small step is required in order to gain an 

 insight into the nature of antitoxin formation. This is the very 

 natural assumption that among the various receptors perhaps by 

 chance the haptophore group of the toxin finds one which possesses 

 an especial affinity for this haptophore group. It is not at all neces- 

 sary that every bacterial toxin should find fitting, i.e. toxophile, 

 receptors in every animal species. On the contrary just this absence 

 of receptors constitutes one of the reasons why certain animal species 

 are immune against certain particular poisons. Furthermore, all 

 the facts indicate that the susceptibility, i.e. the receptiveness, of an 

 organism for a certain toxin is associated with the presence of such 

 toxophile groups of the protoplasm, a point which finds suitable 

 expression in the term receptors. 



As a result of anchoring the toxin molecule by .neans of the 

 haptophore group the cell is influenced in two directions. Primarily 

 owing to the lasting influence of the toxophore group, it sickens, a 

 condition which manifests itself by disturbed functions and possibly 

 by pathological anatomical changes. Besides this, however, in a 

 manner shortly to be discussed, a regenerative process is begun which 

 can lead to the formation of antitoxin. Since this regenerative 

 process can be excited by toxoids lacking the toxophore group, as 

 well as by the toxins themselves, we must assume that it is inti- 

 mately related to the haptophore group. Hence the two parallel 

 processes, antitoxin production and toxic action, are independent in 

 that they are caused by two different groups. In harmony with this 



