DIGESTION OF FOOD. 355 
Tut CHANGES PRODUCED IN THE FooD IN THE ALIMENTARY 
CANAL. 
We have now considered the method of secretion, the secre- 
tions themselves, and the movements of the various parts of 
the digestive tract, so that a brief statement of the results of 
all this mechanism, as represented by changes in the food, will 
be appropriate. We shall assume for the present that the effects 
of the digestive juices are substantially the same in the body 
as in artificial digestion. 
Among mammals food is, in the mouth, comminuted (except 
in the case of the carnivora, that bolt it almost whole, and the 
ruminants, that simply swallow it to be regurgitated for fresh 
and complete mastication), insalivated, and, in most species, 
chemically changed, but only in so far as starch is concerned. 
Deglutition is the result of the co-ordinated action of many 
muscular mechanisms, and is reflex in nature. The csophagus 
secretes mucus, which lubricates its walls, and aids mechan- 
ically in the transport of the food from the mouth to the stom- 
ach. In the stomach, by the action of the gastric juice, food 
is further broken up, the proteid covering of fat-cells is digested, 
and the structure of muscle, etc., disappears. Proteid matters 
Fie. 294.—Matters taken from pyloric portion of stomach of dog during digestion of mixed 
food (after Bernard). a, disintegrated muscular fibers, strize havin; sep penned b,c, 
muscular fibers in which strie have partly disappeared ; d, d, d, globules of fat; e, e, e, 
starch ; g, molecular granules. 
