CHAPTER XL 

 PRECIPITINS. 



In the former chapter, the phenomenon of agglutination was explained 

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

 ing 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 production 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. Tschistowitsch 

 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. Whatever 

 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 agglutinoids 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. 



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