DIGESTION. 187 



this mechanical irritation of the mucous coat of the stomach, as 

 well as by the chemical irritation caused by the food and saliva, an 

 increased secretion of gastric juice occurs. The food is thereby 

 freely mixed with liquid and is gradually converted into a pulpy 

 mass, the chyme. This mass is acid in reaction, and with the ex- 

 ception of the interior of large pieces of meat or other solid foods, 

 the chyme is acid throughout. The metabolism products in the 

 digestion of proteids and carbohydrates may always be detected in 

 the chyme ; likewise more or less changed undigested residues of 

 swallowed food, which indeed form the chief mass of the consti- 

 tuents of the chyme. 



In the chyme morsels of FLESH more or less changed are found 

 which, when unboiled flesh is partaken of, may be much swollen 

 and slippery. MUSCLE and CARTILAGE are also often swollen and 

 slippery, while pieces of BONE sometimes show a rough and uneven 

 surface after the digestion has continued for some time, which de- 

 pends upon the fact that the gelatinous substances of the bone are 

 attacked more quickly by the gastric juice than the earthy parts. 

 MILK coagulates in the stomach by the combined action of the 

 rennet enzyme and the acid, but in certain cases by the action of the 

 acid alone. From the relative quantities of the swallowed milk to 

 the other food either large and solid lumps of cheese are formed or 

 smaller lumps or grains which are divided in the pulpy mass. Cow's 

 milk regularly yields large, solid masses or lumps; human milk 

 gives, on the contrary, a fine, loose coagulum or a fine precipitate 

 which is immediately dissolved in part by the acid liquid. The 

 milk-sugar may pass into lactic-acid fermentation, and this accord- 

 ing to RICHET, is the reason why the acid reaction of the contents of 

 the stomach is greater at the end of the digestion of a meal consist- 

 ing mainly of milk. 



BREAD, especially when not too fresh, is converted rather easily 

 into a pulpy mass in the stomach. Other vegetable foods, such as 

 POTATOES, may, if not sufficiently masticated, often be found in the 

 contents of the stomach, very little changed, several hours after a 

 meal. 



STARCH is not converted into sugar by the gastric juice, but in 

 the first phases of the digestion, before a large quantity of hydro- 

 chloric acid has accumulated, it seems that the action of the saliva 



