CLASSIFICATION OF PROTEINS 183 
same chemical structure as the other proteins, but are characterized by 
a great insolubility in all neutral solvents. 
(f) Hvzstones. Soluble in water and insoluble in very dilute ammonia 
and, in the absence of ammonium salts, insoluble even in an excess of 
ammonia; yield precipitates with solutions of other proteins and a 
coagulum on heating, which is easily soluble in very dilute acids. On 
hydrolysis they yield a large number of amino acids, among which 
the basic ones predominate. 
(g) Protamins. Simpler polypeptids than the proteins including the 
preceding groups. They are soluble in water uncoagulable by heat, 
have the property of precipitating aqueous solutions of other proteins, 
possess strong basic properties and form stable salts with strong mineral 
acids, among which the basic amino acids predominate. 
II Conjugated Proteins. Substances which contain the protein 
molecule with nucleic acid. 
(a) Nucleoprotens. Compounds of one or more protein molecules 
with nucleic acid. 
(b) Glycoproteins. Compounds of the protein molecule with a sub- 
stance or substances containing a carbohydrate group other than a 
nucleic acid. 
(c) Phosphoproteins. Compounds of the protein molecule with 
some, as yet undefined, phosphorus containing substance other than a 
nucleic acid or lecithin. 
(d) Hemoglobins. Compounds of the protein molecule with hema- 
tin or some similar substance. 
(e) Lecitho-proteins. Compounds of the protein molecule with 
lecithins (lecithans, phosphatids). 
III. Derived Proteins. 
1. Primary Protein Derivatives. Derivatives of the protein mole- 
cule apparently formed through hydrolytic changes which involve only 
slight alterations of the protein molecule. 
(a) Proteins. Insoluble products which apparently result from the 
incipient action of water, very dilute acids or enzymes. 
(b) Metaproteins. Products of the further action of acids and alka- 
lies whereby the molecule is so far altered as to form products soluble 
in very weak acids and alkalies but insoluble in neutral fluids. 
This group will include the familiar ‘ acid proteins’ and “ alkali 
proteins ’’ not the salts of proteins with acids. 
(c) Coagulated Proteins. Insoluble products which result from (1) 
the action of heat on their solutions, (2) the action of alcohols on the 
protein. 
