IMMUNITY AND SUSCEPTIBILITY. 569 



that it is located within the cell protoplasm and in the flagella. Without 

 doubt, in certain cases this substance is excreted from the cell into the 

 surrounding media, as is shown by the fact that when nitrates of bacterial 

 cultures are injected they frequently give rise to the formation of agglutin- 

 ins. This agglutinogenic substance is specific and varies with the species. 

 There are, however, very closely related substances of this character 

 among some groups of bacteria. When these agglutinogenic substances 

 are injected into the animal they frequently give rise to agglutinins which 

 when combined with other members of this group will produce agglutin- 

 ation in low dilutions. Such a reaction and property is known as "group 

 agglutination" and the agglutinins produced in such a case are known 

 as coagglutinins. For example, the serum of the patient suffering from 

 typhoid fever or of an animal immunized with B. typkosus will produce 

 an agglutination first of B. typhosus, but in addition an agglutination of 

 B. coli, B. paracoli, B. paratyphosus, B. enteritidis, etc. The agglu- 

 tination of these last named organisms, of course, will not be active 

 except in low dilutions, and in order to satisfactorily exclude them it 

 is necessary to dilute the serum to a higher point. This phenomena 

 of coagglutination is due to the fact that there are some chemical sub- 

 stances (agglutinogenic) within these bacteria which are common to all 

 and which give rise to the formation of agglutinins, which are chemically 

 similar to each other in certain respects. 



Structure of Agglutinins and Agglutinogens. According to Ehrlich's 

 conception the agglutinins are composed of two groups, a haptophile 

 or combining group with which it combines with the haptophore group 

 of the agglutinogen and a zymophorous or agglutinophorous group 

 which actually produces the agglutination. The agglutinogen is also 

 composed of a combining group known as the haptophore group with 

 which it combines with the haptophile of the agglutinin. It is probable 

 that this same haptophore group will combine also with various tissue 

 cells and give rise to the formation of agglutinins which are really free 

 haptophile receptors of the tissue cells which have been acted upon by 

 the agglutinogenic substance contained in the bacteria. 



Agglutinoids. It is possible by means of heat and chemicals to destroy 

 the zymophorous group of the agglutinin, leaving only the haptophile 

 group. Such a substance is known as an agglutinoid, being similar to 

 a toxoid. A temperature of not to exceed 60 to 70 is necessary to pro- 

 duce this substance. Agglutinoids will combine with. the agglutinogen 



