148 CHEMISTRY OF IMMUNITY AGAINST BACTERIA 



in defense against infection is, however, questionable, as we have no 

 evidence that the bacterial enzymes cause harm to the infected organ- 

 ism, or that the products of their action are particularly toxic. By pre- 

 venting the assimilation of food by the bacteria, however, antienzymes 

 might inhibit bacterial growth, a possibility that seems not to have 

 been investigated. 



AGGLUTININS AND AGGLUTINATION 



This well-known phenomenon, the clumping or agglutina- 

 tion of bacteria when acted upon by the serum of immunized or 

 infected animals, can hardly be considered as a means of 

 defense, since we have no evidence that it in any way protects 

 the animal. Agglutinated bacteria seem not to be severely 

 injured by the process, and can grow vigorously in agglutina- 

 tive serum. Possibly agglutination favors phagocytosis and 

 lessens dissemination of the infecting organisms, but it is 

 improbable that the influence on the course of infection is great. 

 Agglutination, therefore, may be looked upon as an incident in 

 the infection, rather than as a definite method of resistance. 



For the production of agglutination it is necessary that the 

 bacterial body contain a substance (ctgglutinogeri) which has 

 an affinity for the specific constituent of the serum, agglutinin. 

 Normal serum may contain agglutinin ; e. </., typhoid bacilli 

 are sometimes agglutinated by normal serum, even when it is 

 diluted thirty times, but by immunization this property can be 

 greatly increased until agglutination may be obtained with dilu- 

 tions as high as one to a million. In immunization it is 

 believed that the agglutinogen, which is probably an intracellu- 

 lar constituent of the bacteria, acts as a stimulator to the for- 

 mation of the specific agglutinin. Hence, when we inject 

 extracts of cells containing endotoxins, we secure agglutinins, 

 for the agglutinogens are liberated from the cells under the 

 same conditions as the endotoxins. 



We can obtain agglutinins against nearly all bacteria, includ- 

 ing non-pathogenic forms, but in varying strengths. Agglutinins 

 are found in the blood stream in the highest concentration, but 

 they are also present in the various organs and in the milk. 

 The place of their formation is unknown. Since bacteria con- 

 tained within a collodion sac implanted in an animal give rise to 

 the production of agglutinins, it is evident that the agglutino- 

 gens are diffusible to some extent, at least, through collodion. 

 Old cultures of bacteria contain free agglutinogens, probably lib- 

 erated from disintegrated cells, and filtrates of such cultures will 

 neutralize agglutinins, showing both that the agglutinogens are 

 filterable, and that the reaction of agglutination is a chemical 



