330 PROTEINS 



belongs to a class of compounds described by Hofmeister as 

 pseudo-globulins ; the precipitate formed is a compound of 

 the precipitin with the albumin contained in the serum to which 

 the precipitin was added. The precipitin so prepared should 

 only react with horse serum and not with the serum of any 

 other animal ; the reaction is, however, not absolutely specific, 

 inasmuch as a precipitin may react with the serum of an 

 animal closely related to the one from whose serum it was pre- 

 pared. It has, moreover, been found that substances which 

 had been isolated from natural fluids, as well as native sera, 

 were able to incite a precipitin formation when injected into 

 the blood of some living animal, and it has been thus possible 

 to show that the albumin contained in milk is not identical 

 with that obtained from blood. The method has been em- 

 ployed by Kowarski and Schlitze * for distinguishing the vari- 

 ous plant albumins, and by Rickmann,f Uhlenhuth,J and 

 others for distinguishing between horse flesh and the meat of 

 other animals. An attempt has also been made to employ 

 the same principle for the estimation of proteins by a com- 

 parison of the precipitates formed under various conditions, § 



As illustrating the very close connexion existing between 

 albumins and globulins, it is worthy of note that Moll claims to 

 have converted serum albumin into serum globulin by warming 

 a 3 per cent solution of serum albumin for one hour to 60° C, 

 with N/66 sodium carbonate, but it is difficult to say whether 

 true serum globulin was actually produced. According to 

 Chick and Martin, || however, the conversion of albumin into 

 globulin may be explained merely by assuming a difference 

 in the state of aggregation. 



EXTRACTION OF PROTEINS. 



The main facts relating to the solubilities of the common 

 vegetable proteins are as follows : — 



* Kowarski and Schiitze : " Deut. med. Wochenschr,," 1901, 27, 442; 1902, 

 28, 804. 



t Rickmann ; " Chem. Zeit.," 1907, 2, 1983. 



J Uhlenhuth and Weidanz : " Praktische Anleitung z. Ausfi'hrung des 

 biolog. Eiweissdifferenzierungsverfahren," Jena, 1909. 



§ Schulz : " Deut. med. Wochenschr.," 1906, 32, no. 26 ; " Zeit. Unters. 

 Nahr. u. Genussm.," 1906, 12, 257. 



11 Chick and Martin : " Journ. Physiol.," 1912, 45, 261, 



