IMMUNITY 215 



to add, in the light of the experiments of the Metchnikoff 

 school, by the leucocytes. 



In bacteriolysis and haemolysis as defined by Bordet's 

 experiments, also immunity phenomena, the complement and 

 the amboceptor (or immune-body) come into play. Com- 

 plement is an atom group already present in the body, whereas 

 amboceptor is analogous to the antitoxin : it possesses, how- 

 ever, two haptophore groups, one uniting with the cells (blood 

 corpuscles or bacteria), the cytophil group, the other linking 

 up the complement, the complementophil group. The anti- 

 bodies are receptors or amboceptors set free and detached 

 from the cells which form them. 



It is impossible to follow here all the developments of the 

 side-chain theory. Ehrlich has complicated it almost to 

 excess in order to include in it the infinite complexity of facts 

 observed in experiments with the various antibodies, anti- 

 toxins, haemolysins, bacteriolysins, and the other cytolysins, 

 precipitins, and agglutinins. The dominant idea is always to 

 give a chemical interpretation of nutrition and, as a particular 

 case of this, of immunity. 



The conception was first intended to explain the physiology 

 of toxin and antitoxin action, and it is to this that it is best 

 adapted ; but it has had to undergo complication, not only to 

 include the largest number possible of the ascertained facts, 

 but to act up to its original intention as an explanation in 

 terms of chemistry. 



It is to explain all these facts 1 that the distinction between 



1 For example these, that the broth culture of the diphtheria bacillus 

 which constitutes crude toxin is not a simple substance : nor is there any 

 reason to believe that the broth cultures of the tetanus bacillus is any 

 more so, since it contains at least two poisons, tetanolysin and tetano- 

 spasmin. The products of cell-life are frequently very complex : Ehrlich, 

 for example, quotes with justice cinchona bark with its twenty odd 

 alkaloids and the liver cells with their round dozen ferments. 

 Toxin left to itself, even protected from light and heat, rapidly becomes 

 modified : it feels the effect of age and not only deteriorates in activity but 

 undergoes qualitative changes. Toxin acts after a period of incuba- 

 tion. The neutralization by antitoxin no longer proceeds in the same 

 way when the appropriate dose of antitoxin is added hi separate fractions 

 instead of all at once (Danysz-Dungern phenomenon). 



