676 PHYSIOLOGICAL CHEMISTRY. 



Peptone is the end-product of gastric digestion, is diffusible, and 

 is not further changed by pepsin. The intermediate products exist 

 at the same time in gastric digestion, their relative quantities depend- 

 ing on tiie length of time the action has progressed. 



While it is believed that gastric digestion normally carries the de- 

 composition of proteins no further than this, it is possible to split 

 proteins into the amino-bodies by pepsin-hydrochloric acid digestion 

 outside of the body. 



Compound proteins are split by gastric juice, the simple proteins 

 formed being digested as above stated. The nucleoproteins yield a 

 peptone free from phosphorus, the nuclein split off being unchanged. 

 Collagen is first converted into gelatin, which then forms successively 

 an acid albumin, proto-proteose, deutero-proteose, and gelatin-peptone. 

 Elastin is changed slowly, while keratins are not changed at all. 



Rennin is a milk-curdling enzyme present in all normal human 

 gastric juice. It is absent in chronic catarrh of the stomach and 

 other diseases. Its presence in gastric juice is shown by its action 

 on milk, and will be considered in the article on clinical examination 

 of gastric juice. 



Absorption in the stomach. It has been shown that the stomach is 

 able to absorb sugars, peptones, salts, and some drugs. However, 

 the absorption is not extensive unless concentrated solutions are 

 present, and probably plays no great part in normal metabolism. 



Experiment 80. (Artificial gastric digestion.) Dissolve 2 grammes of scale 

 pepsin in 1000 c.c. of 0.4 per cent, hydrochloric acid. To this solution add 

 about 250 grammes of protein. The protein material may be fresh or dried 

 blood-fibrin, the meat- residue from the preparation of creatine (Experiment 77), 

 or the whites of 18 eggs, previously boiled and finely divided. The fresh fibrin 

 or the egg-albumin may be added directly to the digestive fluid. The meat- 

 residue or dried fibrin should first be boiled with a liter of water, containing 

 1 c.c. of hydrochloric acid, until the material gelatinizes ; it must be cooled 

 before mixing it with the digestive fluid. Keep mixture in a thermostat at a 

 temperature of 40 C. (104 F.) for ten days. Filter the solution, heat the 

 filtrate to 50 C. (122 F.), and neutralize with sodium carbonate, when syntonin 

 is precipitated. 



Evaporate filtrate from syntonin to about 200 c.c., adding sodium carbonate 

 if necessary to keep solution neutral during evaporation, filter, and saturate 

 solution with ammonium sulphate, when protease is precipitated, while peptone 

 remains in solution. 



To purify the proteose, dissolve the precipitate in water, heat to boiling, and 

 add barium carbonate until all ammonium sulphate is decomposed. Filter, 

 evaporate filtrate to a small volume, and pour solution into double the volume 

 of 95 per cent, alcohol, when proteose is precipitated as a sticky mass. To 

 obtain it as a powder, allow the mass to remain in contact with the alcohol for 



