NEUTRALISATION OF H^MOLYSINS 183 



has been found to have a very high value and to change 

 greatly with temperature, so that evidently here greater 

 transformations take place during the course of time. 



In order to explain this peculiarity of the toxin, Ehrlich 

 originated his so-called side chain theory, which has 

 played a great role in these matters, especially in the 

 German literature. Organic chemistry teaches us that 

 certain properties of different substances, for instance the 

 property of giving coloured solutions, depend upon the 

 presence in these substances of the same group of atoms ; 

 in this special case this group is called the chromophoric 

 group. The other parts of the molecule may be rather 

 different in the different substances with the same prop- 

 erty, and therefore this function is considered to be, 

 so to speak, located in the common group. Now the 

 poisons possess the two common properties of being 

 poisonous and of binding their antitoxins, and these two 

 properties do not vary with each other ; as we have seen, 

 the poisonous attribute diminishes more rapidly than the 

 other in a solution of tetanolysin, and the same is the case 

 with diphtheria-toxin, the study of which led Ehrlich to his 

 conceptions. Ehrlich therefore expresses this peculiarity 

 in the following manner. The two said properties belong 

 to two different groups, called the toxophoric group, which 

 is poisonous, and the haptophoric group, which binds anti- 

 toxin. In the molecule of the poisonous substance, which 

 we suppose to be composed of very many atoms, the two 

 groups lie rather far from each other, so that chemical 

 changes may take place in the one group the toxophoric 

 without influencing sensibly the function of the other 

 group. To express this Ehrlich supposes that the two 



