220 INFECTION AND IMMUNITY. 



ance of agglutinin from the serum, which may be 

 demonstrated, shows that something in the bac- 

 teria (agglutinogen) has combined with the ag- 

 glutinin. 

 Distribution The location of agglutinogen in the bacterial 



of Agglnti- ,, , . , & ,. m , 



no&en. cells has received some discussion. There is a tend- 

 ency to believe that it exists in the cell envelope or 

 perhaps on its surface. It appears to be formed in 

 the cell, and, in some cases, it may be excreted into 

 a surrounding medium; certainly when bacteria 

 die and disintegrate agglutinogen is liberated. The 

 filtrates of certain cultures (entirely free from 

 bacterial cells), when injected into animals, will 

 cause the formation of agglutinins. Also, just as 

 a micro-organism is able to absorb agglutinin from 

 the corresponding antiserum by a process of 

 chemical union, so a filtrate of the type mentioned 

 is able to neutralize the agglutinating power of the 

 serum. In these instances, agglutinogen becomes 

 free as a consequence of disintegration of some of 

 the bacterial cells. 



The Precipi- The filtrates of certain cultures exhibit another 

 Reaction phenomenon when they are mixed with their spe- 

 cific antiserums; this has to do with the bacterial 

 precipitins of Kraus. If, for example, the filtrate 

 of an old typhoid bouillon culture is mixed with 

 antityphoid serum, a distinct precipitate is formed 

 which eventually settles to the bottom of the tube. 

 This is a specific reaction, and does not occur if the 

 filtrate is mixed with some other immune serum. 

 It is thought by some that this so-called precipi- 

 table substance in the filtrate is identical with the 

 agglutinable substance (agglutinogen), but this 

 point is still the subject of investigation. 



