130 THE PROTEINS AND THE AMINO-ACIDS 



jectural group of substances, for although proteins associated with 

 phospholipins have been prepared from yolk of egg, and from vegetable 

 tissues, it is not yet certain whether the phospholipin is an integral 

 part of the protein molecule, or merely a contamination which "is 

 physically adherent to it. Evidence of an electrochemical character 

 has demonstrated, however, that compounds between lecithin and 

 proteins are formed when the two substances are mixed in aqueous 

 solution, and we may infer that similar compounds may not improbably 

 exist in nature. 



HI. THE PRODUCTS OF PROTEIN HYDROLYSIS. 



Infraproteins. The infraproteins are substances produced in the 

 initial stages of protein hydrolysis which still retain the characteristic 

 properties of the proteins. Examples are the Acid- and Alkali-albumin- 

 ates, formed from albumins by gentle heating in acid or alkaline solu- 

 tions, and which differ from albumins in being insoluble in neutral 

 distilled water. Other examples are Paracasein, formed by the action 

 of rennet or weak pepsin upon casein, and the Paranucleins which are 

 formed by the partial digestion of a variety of phosphoproteins. 



Proteoses. The proteoses are hydrolytic cleavage-products of the 

 proteins which have lost the characteristic protein property of being 

 coagulable by heat, but they retain the coagulability by ammonium 

 sulphate. They are usually subdivided into Primary Proteoses which 

 are coagulable by half-saturation of their solutions with ammonium 

 sulphate, and Secondary or Deuteroproteoses which are coagulated by 

 complete saturation of their solutions with ammonium sulphate. The 

 majority of the proteoses are coagulable by alcohol, but certain of them 

 are soluble in alcohol. They yield a reddish violet or pink biuret- 

 reaction. 



A considerable number of the proteoses are toxic when injected into 

 the circulation, while the native proteins with a few marked exceptions, 

 such as the Ricin in castor-oil beans (Ricinus Communis) are non-toxic. 

 On the other hand the native proteins are Antigenic that is, they give 

 rise, on repeated injection into the circulation of animals, to sub- 

 stances which circulate in the blood serum and have the property of 

 precipitating the particular protein against which the animal has 

 been immunized. The proteoses on the contrary are as a rule non- 

 ant igenic. 



Peptones. The peptones are still simpler products of the hydrolytic 

 cleavage of proteins. They are slightly diffusible, and they are inco- 

 agulable either by heat or by ammonium sulphate. They are, however, 

 precipitable by tannic acid, phosphotungstic acid or lead acetate. 

 They are usually coagulable by alcohol, although certain peptones, 

 especially when combined with acid, are not coagulable by alcohol. 

 They yield a clear pink biuret-reaction, and are non-antigenic and, as 

 a rule, non-toxic. 



