AGGLUTIN1NS 97 



ascertained that while they can prevent infection when they are 

 introduced together with the organisms or shortly after, they are of 

 little if any apparent avail in combating an already established 

 infection. Why this should be is not clear, unless we assume that 

 the organisms have developed new characteristics, in consequence of 

 which they are no longer open to attack by the bacteriolysins of the 

 serum, and that the subsequent defence of the body must be carried 

 on by other forces. For the correctness of this view there is some 

 actual basis (see preceding chapter), but even so the last word on 

 the use of the bacteriolytic sera has probably not yet been 

 spoken. 



But in any event the discovery of the bacteriolysins must be 

 regarded as one of the greatest importance, as it has enabled us to 

 gain a certain insight into the defensive mechanism of the animal 

 body, which is most essential to further advance. Practically impor- 

 tant is the fact that the action of the bacteriolytic immune ambo- 

 ceptors is specific and thus permits of a twofold diagnostic application. 

 As the amboceptor content of the immunized animal is always higher 

 than that of the normal control, a higher titer in reference to a given 

 organism may be regarded as evidence of a preceding or existing 

 infection. Similarly one can use an immune serum for the purpose 

 of identifying a given organism, by comparing its action with that 

 of a normal serum upon the organism in question, in the peritoneal 

 cavity of a guinea-pig. Both methods are in actual use, the first for 

 ascertaining whether or not an individual has recently passed through 

 an attack of cholera, the other for establishing the identity of the 

 corresponding organism after its isolation from the feces. (For a 

 description of the method see Diagnostic Bacteriolytic Reactions.) 



Agglutinins. The next group of antibodies was discovered by 

 Gruber and Durham (1896). These are termed agglutinins from the 

 fact that the sera in question, when brought together with emulsions 

 of the corresponding organisms, will cause the "clumping" or agglu- 

 tination of the bacteria, and if these are normally motile, incidentally 

 affect their loss of motility. As this property also is specific within 

 certain limitations and the technique involved in its demonstration 

 very simple, the principle has been extensively utilized for diagnostic 

 purposes. As in the case of the bacteriolysins it may be applied 

 both for the identification of a given organism and in search for the 

 corresponding agglutinin. Under the name of the Widal reaction the 

 7 



