SPECIAL PROPERTIES OF BLOOD SERUM. 2/5 



cerned with the results of experiments, with facts about which 

 there cannot be much question. But a comprehensive theory 

 to correlate all these generalizations became necessary. Many 

 attempts have indeed been made to establish a theoretical basis 

 for the doctrines of immunity, but it remained for Ehrlich to 

 suggest something which is really tangible from the chemical 

 standpoint. To follow the Ehrlich notions some other mat- 

 ters must be explained first. 



Years ago in attempting to explain some of the properties 

 of large organic molecules, Pasteur introduced the notion of 

 molecular asymmetry into chemical science. He showed the 

 value of the notion of configuration in dealing with certain 

 classes of chemical problems. This general idea was greatly 

 advanced by Emil Fischer in his papers on the chemistry of 

 the sugars. Certain ferments were found to decompose one 

 sugar of an isomeric group, but to leave the other almost iden- 

 tical sugars untouched. In other words the ferments were 

 found to observe a specific selection, and to work as ferments, 

 the enzymes in question must possess a certain stereochemical 

 structure bearing some relation to the stereochemical structure 

 of the sugar. Without this relation fermentation cannot take 

 place. In order to make his meaning plain Fischer employed 

 a figure which has since become famous. He said, in speak- 

 ing of certain glucosides, " Enzyme and glucoside must fit into 

 each other as a key into a lock in order that the one may be 

 able to exert a chemical action on the other." In one of his 

 papers Fischer suggested that the idea of related molecular 

 configuration of ferment and fermentable body may prove of 

 value in physiological investigations as well as in chemistry 

 and in the development of the theory of Ehrlich this predic- 

 tion has been verified. Toxins and anti bodies combine with 

 each other only when they possess corresponding atom groups, 

 and specificity is regarded as dependent on this relative con- 

 figuration. 



Without going into minute details the chemical part of the 

 Ehrlich theory is briefly this. Bacteria, animal cells and tox- 



