PROTEINS 97 



the chief organic constituent of bone. It occurs also in cartilage. 

 There probably are several collagens. Collagen, if boiled with 

 water or dilute acid, is converted into gelatine. Collagen is in- 

 soluble in water, dilute salt solutions, dilute acids and alkalies. 



Gelatine, obtained by boiling collagen, swells up in cold water, 

 but dissolves in hot. If sufficiently concentrated, such a solution 

 will set, on cooling, to a jelly. Gelatine is not coagulated by 

 boiling, nor will it precipitate on the addition of strong mineral 

 acids or metallic salts. It may be precipitated by a variety of 

 reagents, however, such as alcohol, tannic acid, etc. Gelatine 

 gives the biuret reaction, but it contains neither tyrosine nor 

 tryptophane, and thus if pure will not give the Millon or 

 Adamkiewicz tests. Gelatine contains much glycocoll. After 

 prolonged boiling, a gelatine solution will no longer gel on cooling. 



Elastin. Elastin occurs in connective tissue, and in largest 

 amount in the cervical ligament. Fresh elastin forms yellow- 

 ish shreds or strings which are elastic in character. It is in- 

 soluble in water and most of the protein solvents. Elastin con- 

 tains large amounts of glycocoll and leucine. It does not give 

 the Adamkiewicz test. 



Histones. The histones are found chiefly in the sperma- 

 tozoa of fish, but the globin portion of the hemoglobin of the 

 blood is usually classed in this group. Their chief character- 

 istic is a high percentage of diamino acids. In this respect they 

 stand midway between the protamines and the remaining simple 

 proteins. They are basic in nature. The group is not sharply 

 defined. 



Protamines. The protamines are the most basic of the pro- 

 teins. They occur in the ripe spermatozoa of fish. They are 

 named from their origin,, as salmine, from the salmon, sturine 

 from the sturgeon, etc. They are characterized by their high 

 percentage of diamino acids, particularly arginine. Salmine 

 contains 87% of arginine. As a result, solutions of protamines 

 in water are alkaline in reaction. They give the biuret test, but 

 most of them do not give the other color tests for proteins. 



