AGGLUTININS 243 



respond to the stimulus. The substance within the intro- 

 duced cell which acts as a stimulus (antigen) to the body 

 cells is called an "agglutinogen." That "agglutinogen" is 

 present in the cell has been shown by injecting animals exper- 

 imentally with extracts of cells (bacterial and other cells) 

 ai\.d the blood serum of the animal injected showed the 

 presence of agglutinin for the given cell. It will be noticed 

 that the receptors which become the free agglutinins have 

 at least two functions, hence at least two chemical groups. 

 They must combine with the foreign cells and also bring 

 about their clumping together, their agglutination. Hence 

 it can be stated technically that an agglutinin possesses a 

 haptophore group, and an agglutinating group. 



The formation of agglutinin in the body for different bac- 

 teria do^s not as yet appear to be of any special significance 

 in protecting the animal from the organism, since the bac- 

 teria are not killed, even though they are rendered non- 

 motile, if of the class provided with flagella, and are clumped 

 together. The fact that such bodies are formed, however, 

 is of decided value in the diagnosis of disease, and also in 

 the identification of unknown bacteria. 



In many bacterial diseases, agglutinins for the particular 

 organism are present in the blood serum of the affected 

 animal. Consequently if the blood serum of the animal be 

 mixed with a suspension of the organism supposed to be the 

 cause of the disease and the latter be agglutinated, one is 

 justified in considering it the causative agent, provided cer- 

 tain necessary conditions are fulfilled. In the first place it 

 must be remembered that the blood of normal animals fre- 

 quently contains agglutinins ("normal agglutinins") for 

 many different bacteria when mixed with them in full 

 strength. Hence the serum must always be diluted with 

 physiological salt solution (0.85 per cent.). Further, closely 

 related bacteria may be agglutinated to some extent by the 

 same serum. It is evident that if they are closely related, 

 their protoplasm must contain some substances of the same 

 kind to account for this relationship. Since some of these 

 substances may be agglutinogens, their introduction into 

 the animal body will give rise to agglutinifis for the related 



