82 THEORY OF FEEDING. 



in the mouth therefore appear to be more mechanical than 

 chemical. 



DIGESTION IN THE STOMACH. 



It is probable that the presence of saliva, which is an 

 alkaline fluid, is beneficial in checking undue acidity in the 

 stomach. Respecting the action of a cell-membrane dissolving 

 ferment, see page 68. 



The digestion of the nitrogenous matter of the food begins 

 in the stomach and is carried on by the action of pepsin, which 

 is a ferment found in the gastric juice, and which has the 

 property of changing nitrogenous matter into a soluble form 

 (peptone). It also serves to split up vegetable fat into a fine 

 state of division by dissolving the nitrogenous envelopes 

 which enclose the globules of fat. The natural and healthy 

 acidity of gastric juice is chiefly due to the presence of 

 hydrochloric acid, which confers antiseptic properties on 

 gastric juice, as we may see by the immunity with which 

 many races of men eat putrid flesh and decomposing fish. 

 Gastric juice contains about 97.3 per cent, of water, and about 

 .3 per cent, of hydrochloric acid (Schmidt). 



The presence of food in the stomach acts as a stimulant 

 to the secretion of gastric juice, which at first flows slowly 

 into that organ, but more quickly later on. Its secretion is 

 liable to become checked by exercise, by excitement, or by 

 the stomach becoming unduly distended. It is evident from 

 our knowledge of the distribution of blood in the body (p. 7), 

 that stimulation of the muscles and organs of breathing from 

 exercise, or of the brain from excitement, will produce more 

 or less congestion of blood in these parts, and anaemia in 

 other organs, which cannot perform their work efficiently 

 without a copious supply of blood. Undue distension of the 

 stomach or intestines causes anaemia by pressure, as for 

 instance, when the animal consumes large quantities of boiled 



