1 10 IMMUNE SERA 



a very highly active serum reacts with the blood of 

 all the mammalia. In that case, of course, only a 

 faint clouding is produced even after considerable 

 time. Nuttall also obtained antisera, each of which 

 was specific for one of the large animal classes 

 (birds, reptiles, amphibia). Here, too, the same 

 quantitative differences were noted. 



Nature of the Precipitins. The precipitins are 

 fairly resistant bodies, whose power gradually 

 declines at a temperature of 60 C., but is not lost 

 until 70 C. is reached. Once their action is lost, 

 it cannot be restored by the addition of normal sera, 

 showing that the precipitins, like the agglutinins, 

 are receptors of the second order and are not ambo- 

 ceptors. The resulting precipitate is soluble in 

 weak acids and alkalies. Peptic digestion destroys 

 the substances which effect the precipitation. 

 Leblanc found that the precipitins were precipitated 

 from the serum in that fraction which Hofmeister 

 calls the pseudo globulins. Eisenberg, on the other 

 hand, in his experiments found them in the eu- 

 globulin fraction. The latter result was also obtained 

 by Obermayer and Pick in precipitins obtained 

 from goats and rabbits. The discordant results 

 are comprehensible in view of recent publications 

 concerning the unreliability of ammonium sulphate 

 fractionation of serum globulins. The nature of 

 the resulting precipitate has also been studied by 

 Leblanc. He finds that it is a combination of the 



