PROTEINS 241 



(b) Place a few pieces of horn in a few cubic centimeters each 

 of artificial gastric and pancreatic juice, add a small amount of 

 toluol, and set in the incubator until the next period. Horn is 

 not digested by gastric or pancreatic juice. Conclusions as to 

 the digestibility of horn are drawn from the appearance of the 

 pieces. It is not possible to use the color, tests for ascertaining 

 whether or not horn has been digested, as the pancreatic and 

 gastric ferment preparations themselves contain soluble proteins 

 in amounts sufficient to give positive color reactions. 



(c) Suspend small pieces of horn in water and try the Millon 

 and xanthoproteic tests. Test for loosely combined sulphur. All 

 of these tests should be positive. 



ii. 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. 



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. 

 The gelatine dissolves. On cooling, if the solution is concen- 

 trated, it solidifies to a jelly. 



Gelatine digests in gastric and pancreatic juice. 



iii. 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. 



6. Histones. The globin which forms a part of the hemo- 

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



