IX.] 



GASTRIC DIGESTION. 



73 



3. Hydrochloric Acid of 0-2 per cent. Add 6.5 cc. of ordinary com- 

 mercial hydrochloric acid to I litre of distilled water. 



4. Products of Peptic Digestion and its Conditions. 



(a.) Half fill three large test-tubes, labelled A, B, C, with 

 hydrochloric acid 0.2 per cent. Add to each five drops of glycerin 

 extract of pepsin. Boil B, and 

 make C faintly alkaline with 

 sodic carbonate. The alkalinity 

 may be noted by adding pre- 

 viously some neutral litmus 

 solution. Add to each an equal 

 amount a few threads of well- 

 washed fibrin which has been 

 previously steeped for some time 

 in 0.2 per cent, hydrochloric 

 acid, so that it is swollen up 

 and transparent. Keep the 

 tubes in a water-bath (fig. 42) 

 at 40 C. for an hour, and ex- 

 amine them at intervals of 



FIG. 42. Digestion-Bath. 



twenty minutes. 



(b.) After five to ten minutes, 

 or less, the fibrin in A is dissolved, and the fluid begins to be 

 turbid. In B and C there is no change. Even after long exposure 

 to 40 C. there is no change in B and C. After three-quarters of 

 an hour filter A and part of B and C. Keep the filtrates. 



(c.) Carefully neutralise the filtrate of A with dilute caustic 

 soda = a precipitate of acid-albumin. Filter off this precipitate, 

 dissolve it in 0.2 per cent, hydrochloric acid. It gives proteid 

 reactions (Lesson I. 7). 



('/.) Test the filtrate of (c.) for atbumose or proteose. Repeat 

 all the tests for albumose (Lesson I. 10). Albumose is soluble in 

 water, and gives all the ordinary proteid reactions. It is precipi- 

 tated by nitric acid in the cold in presence of NaCl, but the 

 precipitate is redissolved with the aid of heat, and reappears on 

 cooling. This is a characteristic reaction. It is precipitated by 

 acetic acid and ferrocyanide of potassium ; by acetic acid and a 

 saturated solution of sodic sulphate ; and by metaphosphoric acid : 

 while peptones are not. It gives the biuret reaction (like peptone). 

 Like peptones, it is soluble in water. 



(e.) To part of the filtrate of (c.) add neutral ammonium sul- 

 phate to saturation. This precipitates all the albumoses, while 

 the peptones are not precipitated, but remain in solution. Filter 

 and test the filtrate for peptones (Lesson I. 10). In the biuret 



