130 PRECIPITINS 



It is interesting to note that the proteid contained in the lens of the eye 

 belongs to this class of modified proteids which possess constitutional, 

 but no species specificity. A serum produced by immunization with lens 

 substance will react with the proteid derived from the lens of any animal, 

 but with no other animal proteid. 



In conclusion, the origin of the precipitate formed during the 



Origin of precipitation reaction is of interest. When a very strong 



Precipitate, precipitating serum is employed, the precipitinogen is so 



greatly diluted that it no longer gives any of the chemical 

 reactions for proteids, but nevertheless yields a heavy precipitate when the 

 precipitating serum is added. This surely cannot come from the small 

 trace of proteid in the precipitinogen. Furthermore, if the immune 

 serum is diluted, the formed precipitate becomes comparatively weaker 

 and disappears entirely if dilution is increased. It is, therefore, generally 

 considered that the precipitate originates from the immune serum. 



