632 PHYSIOLOGICAL CHEMISTRY. 



alkali metaproteins have decided acid properties, as can be shown by 

 the fact that on the addition of calcium carbonate they dissolve in 

 water with the liberation of carbon dioxide, a property not possessed 

 by acid metaproteins. 



As part of the nitrogen is eliminated during the formation of alkali 

 metaproteins, the latter cannot be converted into acid metaproteins by 

 treatment with acids ; the reverse change, however, may be brought 

 about. 



(c) Coagulated proteins. Insoluble products, which result from 

 the action of heat on their solutions, or from the action of alcohols on 

 the protein. The nature of the process of coagulation is unknown ; 

 the result is the formation of protein substances insoluble without 

 decomposition. In the liver and other glands coagulated proteins 

 have been found. Hard-boiled white of egg and fibrin are coagu- 

 lated proteins. 



The temperature of coagulation is constant for any certain protein ; 

 it is, however, considerably modified by the presence or absence of 

 acids, alkalies, and salts in the solution. Fractional coagulation by 

 gradual heating of a solution of several proteins aifords a rough means 

 of separation. 



2. Secondary protein derivatives. 



Products of the further hydrolytic cleavage of the protein mole- 

 cule by acids, alkalies, superheated steam, or enzymes. 



(a) Proteoses. Soluble in water, uncoagulated by heat, and pre- 

 cipitated by saturating their solutions with ammonium sulphate or 

 zinc sulphate. 



Primary proteoses (protalbumoses) are precipitated by one-half 

 saturation with ammonium sulphate. 



Secondary proteoses (deutero-albumoses) are precipitated by com- 

 plete saturation with ammonium sulphate. 



There are several subdivisions of primary and secondary proteoses, 

 viz., hetero-proteoses, dysproteoses, the different properties of which 

 are not definite. 



(6) Peptones. Soluble in water, uncoagulated by heat, and not 

 precipitated by saturating their solutions with ammonium sulphate. 

 They are the result of the digestion of proteins ; their solutions in 

 water are readily diffusible. The peptones are divided into anti-pep- 

 tones, hemi-peptones, and ampho-peptones. Here, again, the proper- 

 ties of the different classes are not definite. 



The proteoses and peptones give a biuret reaction showing more 

 red color than the natural proteins. 



