2 80 DIGESTION. 



Changes of the Food in the Stomach. 



The general effect of digestion in the stomach is the 

 conversion of the food into chyme, a substance of various 

 composition according to the nature of the food, yet always 

 presenting a characteristic thick, pultaceous, grumous con- 

 sistence, with the undigested portions of the food mixed 

 in a more fluid substance, and a strong, disagreeable acid 

 odour and taste. Its colour depends on the nature of the 

 food, or on the admixture of yellow or green bile which 

 may, apparently, even in health, pass into the stomach. 



Reduced into such a substance, all the various materials 

 of a meal may be mingled together, and near the end of 

 the digestive process hardly admit of recognition ; but the 

 experiments of artificial digestion, and the examination of 

 stomachs with fistulas, have illustrated many of the changes 

 through which the chief alimentary principles pass, and 

 the times and modes in which they are severally disposed 

 of. These must now be traced. 



The readiness with which the gastric fluid acts on the 

 several articles of food is, in some measure, determined by 

 the state of division, and the tenderness and moisture of 

 the substance presented to it. By minute division of the 

 food, the extent of surface with which the digestive fluid 

 can come in contact is increased, and its action proportion- 

 ably accelerated. Tender and moist substances offer less 

 resistance to the action of the gastric juice than tough, 

 hard, and dry ones do, because they may be thoroughly 

 penetrated by it, and thus be attacked not only at the 

 surface, but at every part at once. The readiness with 

 which a substance is acted upon by the gastric fluid does 

 not, however, necessarily imply the degree of its nutritive 

 property ; for a substance may be nutritious, yet, on 

 account of its toughness and other qualities, hard to 

 digest ; and many soft, easily digested substances contain 

 comparatively a small amount of nutriment. But for a 



