ANALYSIS OF PROTEIN CONSTITUENTS OF CHEESE. 377 



magnesium carbonate cause a partial decomposition of the 

 amides. The author prefers to operate on a portion of the 

 hot-water extract. 



V. Nitrogen in the Form of Amino Acids. — This is 

 taken to be the nitrogen belonging to those compounds in the 

 cheese which are not precipitated by phospho-tungstic acid, and 

 which are not ammoniacal compounds. An amount of the sand 

 mixture, corresponding to 5 grammes of cheese, is mixed with 

 150 c.c. of water, and well shaken for fifteen minutes in a closed 

 vessel. After standing for fifteen, hours at the ordinary tem- 

 perature, 100 c.c. of dilute sulphuric acid (1 vol. : 3 vols, water) 

 are added, and phospho-tungstic acid so long as a precipitate 

 results. The liquid is filtered, the precipitate washed with 

 dilute sulphuric acid until the filtrate amounts to 5l.i(J c.c, and 

 the nitrogen is determined in 200 c.c. of this. By deducting 

 from the amount that previously found as ammoniacal 

 nitrogen, the nitrogen present in the form of amino acids is 

 found. 



VI. Indigestible Nitrogenous Substances. — Tlif ficsh 

 mucous membrane of six pigs' .stomachs is cut into small frag- 

 ments and mixed with water and hydrochloric acid in a wide- 

 necked flask in the proportion of -5 litres of water and I'tO c.c. 

 of 10 per cent, (by weight) hydrochloric acid to each stomach. 

 At the same time, 21 grammes of thymol dissolved in alcohol 

 are added as a preservative. The mixture is left for twenty- 

 four hours, with occasional shaking, and then filtered through 

 flannel, coarse paper, and fine paper successively. If necessary, 

 the amount of hydrochloric acid in the extract is brought to 

 exactly 0'2 per cent. As thus prepared, the gastric juice remains 

 unaltered for months. 



Sand mixture, containing 5 grammes of cheese, is deprived of 

 its fat by extraction with ether, mixed with 500 c.c. of gastric 

 juice in a beaker, and the mixture warmed for forty-eight 

 hours in a thermostat at 37'' to 40"" C. (99° to h^i' ¥.). At 

 intervals of about two hours, 5 c.c. of 10 per cent, hydrochloric 

 acid are added, until the acidity of the whole reaches 1 per cent. 

 The liquid is filtered through paper or asbestos, the residue 

 washed with water, and the nitrogen in it determined. 



VII. Nitrogen in the Form of Albumose and Pep- 

 tones. — A weighed quantity of the sand mixture, containing 

 5 grammes of cheese, is extracted by boiling with successive 

 portions (100 c.c.) of water, the liquid made up to 5iX) c.c. and 

 filtered ; and 200 c.c. of the clear filtrate (mixed with an equal 

 volume of dilute sulphuric acid) are precipitated by phospho- 

 tungstic acid. The precipitate is collected on a filter, washed, 

 and the nitrogen estimated by Kjeldahl's method. 



