CHAPTER XV. 



PRECIPITINS. 



Because of their scientific importance and cer- 

 tain practical features, the serum-precipitins 

 should receive something more than the incidental 

 mention which has been given them under agglu- 

 tination and in other chapters. 



In 1897 ' & aus discovered that bouillon cultures 

 of the organisms of typhoid, cholera and plague, 

 from which the bacteria had been removed by fil- 

 tration, would cause precipitates when mixed with 

 their respective antiserums. The reaction is spe- 

 cific. As stated later, however, this specificity 

 holds only when those quantitative relationships 

 are observed which were found so essential for the 

 agglutination test. The precipitins of Kraus are 

 the bacterial precipitins. He proposed their use 

 for the identification of micro-organisms. If, for 

 example, one has in hand a culture which he sus- 

 pects to be that of the typhoid bacillus, it may be 

 grown in a liquid medium, the cells removed by 

 filtration, and the filtrate mixed with a known 

 antityphoid serum; if a precipitate occurs when 

 the serum is sufficiently diluted, the reaction indi- 

 cates that the organism in question is the typhoid 

 bacillus. Inasmuch as precipitins are formed dur- 

 ing the course of some infections it may be possible 

 to use them in clinical diagnosis, but for either 

 bacterial or clinical diagnosis the agglutination 

 test is more readily performed and interpreted. 



