228 PRECIPITOID 



investigated the formation of an antitoxin for eel serum by inject- 

 ing that substance into rabbits, and found the serum thus obtained 

 not only neutralized the toxic effects of the eel serum, but formed 

 a precipitate with it. In an exactly similar way, he prepared a 

 precipitating serum to a non-toxic serum that of the horse and 

 investigated its properties. He found that the precipitate formed 

 by the interaction of the antiserum and its antibody was soluble in 

 dilute acids and alkalis, but insoluble in water, alkaline carbon- 

 ates, and neutral salts. These results were corroborated by Bordet, 

 whose classical researches on the haemolysins were made about 

 this time. He found that the injection of defibrinated fowl's blood 

 into rabbits caused the appearance of agglutinins, haemolysins, and 

 of precipitins in the serum of the latter, so that the fowl's red 

 corpuscles would be first clumped and then laked, after the 

 addition of the immune serum, and this substance, when added to 

 fowl serum, led to the formation of a precipitate. Bordet also 

 demonstrated the formation of a precipitating serum for milk 

 (lacto- serum). These researches were corroborated by Myers, 

 Uhlenhuth, Wassermann and Schiitze, Nuttall, and others, and 

 the reaction has now been very fully studied, and found to be of 

 considerable practical importance. 



Precipitins are in all respects closely analogous to the agglutinins. 

 They are formed under the same conditions i.e. t as a reaction of 

 the cells to a foreign material, probably in all cases of a proteid 

 nature and appear themselves to be proteids. They are destroyed 

 by pepsin and other proteolytic enzymes, and by acids and alkalis. 

 They appear to be allied to or carried by the globulins. When 

 heated they appear to undergo a change into precipitoid, a sub- 

 stance which has the power of combining with the molecules of 

 precipitogen, but which does not precipitate them ; this is shown 

 by the fact that a further addition of precipitin does not cause 

 precipitation, indicating that the effect is not due to a mere 

 weakening of the substance or to its partial destruction. Hence 

 we deduce that the precipitin molecule consists of two portions 

 a thermostable haptophore or combining group, and a thermolabile 

 functionating group, the action of which is necessary for agglutina- 

 tion of the molecules to occur. This change takes place at a 

 temperature of 50 to 60 C., but it also occurs slowly when 

 precipitin solutions are kept at ordinary temperatures, so that these 

 become gradually useless as tests for their antigens ; and the 

 change may be hastened by the action of light or of various 



