288 PHYSIOLOGICAL CHEMISTRY 



diet's solution for sugar, and for phosphates. Casein is one of 

 the chief constituents of cheese, which also contains much fat. 



57. Weigh accurately about 0.2-0.3 gram dry casein and deter- 

 mine its nitrogen content by the Kjeldahl method. 



Recall that unboiled milk gives a positive guaiac test. 

 Nucleoproteins. Nucleoproteins are present in all cells. 

 They may be prepared from various organs and tissues. 



58. Preparation of nucleoprotein from the pancreas. 

 Hammarsten's Method. Grind a piece of fresh beef pancreas 



in the meat grinder, throw the pulp into 200-300 c.c. of hot 

 water, and boil for about ten minutes. Filter hot. The nitrate 

 will be pale yellow and fairly clear. Cool under the tap, and 

 acidify with sufficient acetic acid to make the concentration of 

 acid 0.5-1.0%. The nucleoprotein is precipitated and quickly 

 settles to the bottom. What other groups of proteins are pre- 

 cipitated in this way? Filter off the precipitate, suspend it in 

 200 c.c. distilled water, and add ammonia cautiously until the 

 precipitate has just dissolved. Reprecipitate the nucleoprotein 

 with acetic acid as above. If a pure product is desired, the proc- 

 ess of dissolving in alkali and reprecipitation with acid should be 

 repeated several times. The precipitate is filtered off, washed 

 with water containing a few drops of acetic acid, and then with 

 about 50 c.c. of hot alcohol in small portions (be careful of fire). 

 Spread the washed nucleoprotein upon a carefully cleaned spot 

 on a tile, and manipulate it to remove the alcohol. 



With small portions of the nucleoprotein prepared above per- 

 form the Millon, biuret, and xanthoproteic tests. 



Note that nucleoprotein was not coagulated by boiling. 



59. Fuse a small portion of nucleoprotein with fusion mixture, 

 dissolve the residue in dilute nitric acid and test for phosphorus 

 and iron. 



60. Cover a small portion of nucleoprotein with pepsin solu- 

 tion, and incubate at least 24 hours. Note the undigested 

 residue of nuclein. 



61. Hydrolysis of nucleoprotein. Mix up the remainder of the 

 nucleoprotein with 10 times its volume of 5% hydrochloric acid, 



