278 PHYSIOLOGICAL CHEMISTRY 



28. Collagen. Collagen may be prepared from the tendon of 

 Achilles of an ox by dissolving out the mucoid with lime water. 

 After several days' extraction, the residue is mainly collagen. 

 Collagen is insoluble, only slightly digestible and gives certain of 

 the protein color tests. On boiling for some time it is converted 

 into gelatine. 



29. Properties of Gelatine. With gelatine prepared as above 

 or with commercial gelatine perform the following experiments : 



Test its solubility in cold water. It only swells up. Heat. 

 What happens? On cooling, if the solution is concentrated, it 

 solidifies to a jelly. 



Gelatine digests in gastric and pancreatic juice. 



30. Elastin. Elastin may be prepared from the ligamentum 

 nuchae of the ox. The ligament is cut into small pieces and 

 washed with 10% NaCl two or three times, and then with running 

 water for 48 hours. It is then extracted with half saturated lime 

 water for two days. The material then is boiled for at least two 

 hours with dilute acetic acid to remove collagen. The residue is 

 mainly elastin. It is insoluble, somewhat digestible, exhibits a 

 remarkable elasticity, and responds to several of the protein 

 color tests. 



Histones. The globin which forms a part of the hemoglobin 

 molecule is considered to be a histone by most authorities. It is 

 easily split off from hemoglobin by the action of dilute hydro- 

 chloric acid. 



The histones give the biuret test, usually only a faint Millon 

 reaction, are precipitated from neutral solution by alkaloidal 

 reagents, and form precipitates if added to a protein solution. 

 They are acted on by the digestive juices. They contain a high 

 percentage of diamino acids. 



Protamines. The protamines have been found only in the 

 spermatozoa of fish. The protamines give the biuret test, but 

 most of them give no Millon 's reaction. They are precipitated 

 by alkaloidal reagents, and fairly well by neutral salts. They 

 give precipitates with ammoniacal protein solutions. 



