CHAPTER XI. 



PRECIPITINS. 



In the former chapter, the phenomenon of agglutination was explained 

 as a clumping of bacteria occurring when serum is mixed with its corre- 

 sponding bacteria. In 1897 R- Kraus described a phenomenon, very 

 closely allied to the one just mentioned. He found that when an immune 

 serum, for example, of cholera, typhoid, or pest, is mixed with the clear, 

 sterile nitrate of the respective bouillon cultures of their bacteria (instead 

 of the bacteria themselves), the clear solution becomes turbid, and a 

 precipitate forms. This reaction is known as precipitation; the elements 

 within the immune serum, precipitins; while the substances (antigen) 

 with which the precipitin reacts and which originally stimulated the pro- 

 duction of the precipitin, precipitinogen. 



Like all biological reactions, the phenomenon of precipitation is not 

 limited to bacterial immune sera and culture nitrates, but is observed when 

 any animal, vegetable or bacterial soluble proteid substance is mixed with 

 the serum of an animal which has been immunized against the particular 

 proteid material in question. 



Tschistowitsch and Bordet were the first who called attention to these non-bacterial 

 precipitins. Bordet (1899) found that the blood serum of rabbits treated with the 

 serum of chickens gave a specific precipitate when mixed with chicken serum. Tschi- 

 stowitsch demonstrated a similar reaction with the sera of rabbits treated with horse's 

 and eel serum. 



The biological structure of the precipitins is strongly analogous to that 

 of agglutinins. Many authorities, in fact, consider them identical. What- 

 ever has been said in regard to the effects of heating and addition of acids 

 or alkalies upon agglutinins, applies equally to precipitins. Moreover, 

 they also are composed of two groups, a binding (haptophore) and a 

 functionally active (ergophore) group. If the latter is missing, they are 

 known as precipitinoids, and can interfere with precipitation just as ag- 

 glutinoids do with agglutination. 



In speaking of precipitation, it has always been customary to differen- 

 tiate between bacterial and proteid. For practical purposes this division 

 is superfluous inasmuch as the bacterial precipitins are nothing more than 

 precipitins of bacterial proteids. 



120 



