718 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



tion. The mechanism of the reaction is the same as that of bacterial 

 agglutinins. It is possible that hemoagglutination is one impor- 

 tant factor in the production of agglutination thrombi in certain 

 infectious diseases such as typhoid fever. 



PRECIPITINS. Another group of substances, which are antibodies, 

 is produced through the processes of immunization which have not 

 been definitely connected with the phenomena of immunity. These 

 substances are known as the precipitins. Precipitins may be produced 

 for the protein substances of most bacterial cells and a large variety 

 of other plant and animal cells, such as blood serum, milk and grains. 

 They were first demonstrated in 1897 by Kraus, who noted that the 

 bouillon filtrates of cultures of B. typhosus, Bad. pestis, and Msp. 

 comma would cause precipitates when mixed with the blood serum taken 

 from cases of these diseases. The precipitin reaction is definite and 

 specific. The protein substance used in immunization or concerned 

 in the infection is the only one which is precipitated when the anti- 

 serum is added. To the protein substance which produces the precipi- 

 tins the name precipitinogen is applied. To that substance in the blood 

 serum and body fluids of the immunized or infected animal or person 

 the name precipitin is applied. The combination between the precipi- 

 tinogen and the precipitin forms a new chemical substance known as a 

 precipitate. Precipitin may be formed in various parts of the body, 

 for example, in the parenchymatous cells of the organs and by the 

 leucocytes. Bact. diphtheria will not act as a precipitinogen and 

 will not produce precipitins. This is practically the only bacterium 

 which will not yield these antibodies. 



Normal Precipitins. Precipitins for alien blood serums have been 

 found in the organs and blood of seemingly normal animals. Normal 

 precipitins for bacterial proteins have not been demonstrated to a 

 certainty.' 



Mechanism of the Formation of Precipitins. The mechanism 

 of the formation of precipitins is similar to that of other antibodies. 

 When the precipitinogen is injected into the body of an animal, it 

 combines with certain of the body cells, occupying chemical receptors 

 which otherwise would be used for the taking up of food products. 

 As a result the cells produce new receptors and the number of these 

 more than compensate for the ones already utilized. The chemical 

 receptors are finally thrown off into the body fluids and form the pre- 



