176 PRINCIPLES OF BACTERIOLOGY 



advanced. As in the case of the immune body there is positive proof 

 that the agglutinin combines directly with substances in the bacterial 

 body. 



In some cases the agglutinins are active even in very high dilutions. 

 Thus in typhoid patients and typhoid convalescents a distinct agglu- 

 tination has been observed in dilutions of 1:5000, and this action 

 persisted for months, though not, of course, in the same degree. Even 

 normal blood serurn, when undiluted, often produces agglutination. 

 But the specific agglutinins, which are formed only in consequence of 

 an infection, are characterized by this, that they produce agglutination 

 even when the serum is highly diluted, and, furthermore, that after this 

 dilution the action is specific i. e., the dilution of cholera immune 

 serum agglutinates only cholera bacilli, typhoid immune serum only 

 typhoid bacilli, etc. This specificity, however, as will be shown later, 

 is not always absolute. 



The agglutinating substances when mixed with bacteria are bound 

 to the agglutinable substances in them, the two bodies effecting a loose 

 combination very like toxin and antitoxin. By chemical means it is 

 possible to again separate the agglutinin from the bacteria and use it 

 to agglutinate bacteria anew. 



It was formerly assumed that agglutination was a prerequisite for 

 bacteriolysis. This, however, is not so, for both in cholera and in typhoid 

 immunity bacteriolytic substances have been observed without agglu- 

 tinins, and agglutinating substances without bacteriolysins. 



Of the three antibodies mentioned, serum therapy has thus far made 

 use of the antitoxins; whereas, in serum diagnosis the bacteriolysins 

 and above all the agglutinins are used. Serum diagnosis by means of 

 these two substances was possible only because they had proven them- 

 selves in general as specific. 



Precipitins. If we inject an animal with albuminous bodies of the 

 greatest variety, substances will usually appear in the blood which pos- 

 sess distinct relations to these bodies. They manifest themselves by 

 their power to precipitate the albuminous bodies from dilute solutions 

 in a test-tube. These antibodies are therefore called precipitins. 

 A phenomenon discovered by R. Kraus is probably to be separated 

 from this precipitin action on albumins. This author showed that the 

 serum of a rabbit immunized against typhoid produces a precipitate in 

 the bacterial-free filtrate of a bouillon typhoid culture. This fact has 

 been verified by a number of investigators and found to extend also to 

 other species of bacteria. The precipitins are divided like agglutinins 

 into having group and specific action. 



Characteristics of Agglutinins. As considered by Ehrlich's school, the 

 agglutinin consists of a stable-combining group and an unstable-precipi- 

 tating group. The agglutinable molecule is also believed to consist of 

 two groups, one stable that combines with the agglutinins and one labile 

 that gives the completed reaction. Agglutinins changed by heat, acids, 

 and other influences become agglutinoids, which are comparable to 

 toxoids, complementoids, etc. 



