304 



DIGESTION AND ABSORPTION 



ulates a protein found in milk; after the milk is curdled, the 

 pepsin is able to act upon it. '' Junket" tablets, which contain 



rennin, are used in the kitchen to cause this 

 change. 



The hydrochloric acid fomid in the gastric 

 juice acts upon lime and some other salts 

 taken into the stomach with food, changing 

 them so that they may pass into the blood 

 and eventually form the mineral part of bone 

 or other tissue. The acid also has a decided 

 antiseptic influence in preventing growth of 

 bacteria which cause decay, and some of which 

 might cause disease. 



Movement of Walls of Stomach. — The stomach 

 walls, provided with three layers of muscle which 

 run in an oblique, circular, and longitudinal direc- 

 tion (taken from the inside outward), are well 

 fitted for the constant churning of the food in 

 A peptic gland, from the ^j-^^t organ. Here, as elsewhere in the digestive 

 magrTified.^ a! central t^act, the muscles are involuntary, muscular action 

 or chief cell, which being under the control of the so-called sympathetic 



makes pepsm ; B, bor- ^i^j-pQus system. Food material in the stomach 



der cells, which make , , i j • •, i • ii 



acid. (From Miller's makes several complete cn-cuits durmg the process 



Histology.) of digestion in that organ. Contrary to common 



belief, the greatest amount of food is digested 



after it leaves the stomach. But this organ keeps the food in it in 



almost constant motion for a considerable time, a meal of meat and 



vegetables remaining in the stomach for three or four hours. While 



movement is taking place, the gastric juice acts upon proteins, softening 



them, while the constant churning movement tends to separate the bits 



of food into finer particles. Ultimately the semifluid food, much of it still 



undigested, is allowed to pass in small amounts through the pyloric valve, 



into the small intestine. This is allowed by the relaxation of the ringhke 



muscles of the pylorus. 



Experiments on Digestion in the Stomach. — Some very inter- 

 esting experiments have recently been made by Professor Cannon 

 of Harvard with reference to movements of the stomach contents. 

 Cats were fed with material having in it bismuth, a harmless 



