114 THE BODY AT WORK 



if no attention is devoted to the meal, if no sense of liking accom- 

 panies our offering, my lord the stomach on his part affords the 

 viands an indifferent reception. In consulting our own tastes 

 we are to a large extent consulting the needs of the stomach. 

 Ravenous and excessive feeding is not an exhibition of taste ; 

 it is a return to the instinct of the savage, who was never sure 

 that he would get his full share, and was afraid to trust that 

 another meal would be obtainable when nature declared it due. 

 Some degree of epicureanism is favourable to digestion. The 

 flow of gastric juice in the stomach occurs reflexly in response 

 to the emotion of appetite, to stimulation of the nerves of 

 taste and smell, to the obscure sensations which accompany 

 the activity of the muscles of mastication. 



The gastric juice secreted in a day amounts probably to about 

 8 or 9 pints. To this we must add, when considering the quantity 

 of fluid which passes through the stomach, the saliva, which 

 certainly reaches as much as 2 pints, and the beverages taken 

 with food. 



Gastric juice collected in the manner described above is a 

 clear, colourless, inodorous fluid. It is very acid, and so power- 

 fully peptic as to digest its own weight of coagulated white 

 of egg. Its solid constituents amount to 0-5 per cent. They 

 consist of the two ferments pepsin and rennin, with traces of 

 proteins and mucin, and various inorganic salts. Its acidity 

 is due to free hydrochloric acid to the amount of 0-2 per cent. 

 This acid is more or less in combination with the pepsin. In 

 pure gastric juice hydrochloric acid is the only acid present ; 

 but when mixed with food the juice contains other acids also, 

 especially lactic. 



When food first reaches the stomach, the alkaline saliva 

 which accompanies it neutralizes the acidity of the gastric 

 juice. For some time, probably about half an hour, the 

 conversion of starch into sugar is still carried on by the ptyalin 

 of the saliva, owing chiefly to the difficulty which the gastric 

 juice encounters in permeating the masses of masticated food. 

 The Bacillus acidi laclici is always present in the stomach. It 

 converts some of the sugar into lactic acid ; of this a small 

 quantity is further changed into butyric a N nd acetic acids, with 

 the formation of carbonic acid and hydrogeai gas. After a while 

 the lactic acid is absorbed, and hydrochloric acid alone remains. 



