AGGLUTINATION 487 



brought forward in opposition to this view, and the existence of 

 agglutinoids cannot be said to be completely proved. Like 

 immune-bodies agglutinins are not destroyed at 55 C. (a 

 temperature sufficient to annul bactericidal action), and the 

 question arises as to the relation of the two bodies ; discussion 

 has also taken place as to how far agglutination is an indication 

 of immunity. It may be said that in the case of certain sera 

 investigated it has been shown that the immune-body and the 

 agglutinin are separate substances, and that the agglutinative 

 power does not vary pari passu with the degree of immunity 

 a serum may be strongly agglutinative and feebly bactericidal 

 and vice versa. But while probably as a rule the two substances 

 are distinct, it would not be justifiable to say this is always the 

 case that is, that an immune-body never has an agglutinating 

 action. And while the agglutinative power cannot in itself be 

 taken as the measure of the degree of immunity, agglutinins and 

 immune-bodies are the products of corresponding reactive pro- 

 cesses, and their formation is governed by corresponding laws. 

 Agglutinins become fixed in definite proportion by the receptors 

 of the bacteria ; that is, the agglutinin becomes used up in the 

 process of agglutination, and it has been shown that bacteria 

 may take up many times the amount necessary to their 

 agglutination a corresponding fact to what has been established 

 with regard to immune -bodies of hasmolytic sera. The 

 agglutinins are specific in the sense which has been explained 

 above (p. 466). It can be shown by the method of absorption 

 that in an agglutinating serum there may be several agglutinins 

 with different combining groups, some of which may be taken up 

 by organisms allied to that which has given rise to the anti- 

 serum. Whether or not the combination of an agglutinin with 

 the bacterial receptors is a reversible action must be left an open 

 question. 



Besides those stated above, other phenomena have been 

 observed in the interaction of anti-sera and the corresponding 

 bacteria. For example, it has been shown that when certain 

 bacteria e.g. the typhoid bacillus, b. coli, and b. proteus are 

 grown in bouillon containing a small proportion of the homo- 

 logous serum, their morphological characters may be altered, 

 growth taking place in the form of threads or chains which are 

 not observed in ordinary conditions. In other instances a serum 

 may inhibit some of the vital functions of the corresponding 

 bacterium. 



Precipitins. This subject does not strictly belong to bacteriology, 

 but the general phenomena are so closely allied to those just described, 



