202 GASTRIC DIGESTION 



digested most rapidly, however, are tripe, pigs' feet and brains. Vege- 

 table articles are digested in about the same time as ordinary animal 

 food ; but a great part of the digestion of these substances takes place 

 in the small intestine. Bread is digested in about the time required for 

 the digestion of the ordinary meats. 



Conditions that influence Stomach Digestion. The various condi- 

 tions that influence gastric digestion, except those relating exclusively 

 to the character or the quantity of food, operate mainly by modifying 

 the quantity and quality of the gastric juice. It is seldom that tem- 

 perature has any influence, for the temperature of the stomach in health 

 does not present variations sufficient to have any marked effect on 

 digestion. 



As a rule, gentle exercise, with repose or agreeable and tranquil 

 occupation of the mind, is more favorable to digestion than absolute 

 rest. Violent exercise or severe mental or physical exertion is always 

 undesirable immediately after the ingestion of a large quantity of food, 

 and as a matter of common experience, has been found to retard 

 digestion. 



The effects of sudden and considerable loss of blood on gastric 

 digestion are very marked. After a full meal, the whole alimentary 

 tract is deeply congested, and this condition undoubtedly is necessary to 

 the secretion, in proper quantity, of the various digestive liquids. When 

 the entire quantity of blood in the economy is greatly diminished from 

 any cause, there is difficulty in supplying the amount of gastric juice 

 necessary for a full meal, and disorders of digestion are likely to occur. 

 This is also true in inanition, when the quantity of blood is greatly 

 diminished. In this condition, although the system craves nourishment 

 and the appetite frequently is ravenous, food should be taken in small 

 quantities at a time. 



As a rule children and young persons digest food that is adapted to 

 them more easily and in larger relative quantity than those in adult life 

 or in old age ; but ordinarily in old age digestion is carried on with 

 more vigor and regularity than the other vegetative processes, such as 

 general assimilation, circulation and respiration. 



Influence of the Nervous System on the Stomach. It is well known 

 that mental emotions frequently have a marked influence on digestion, 

 and this, of course, can take place only through the nervous system. 

 Of the two nerves that are distributed to the stomach, the pneumogastric 

 has been the more carefully studied, experiments on the sympathetic 

 being more difficult. The history of the influence of the pneumogas- 

 trics on digestion, however, properly belongs to the physiology of the 

 nervous system. 



