41. That the natural temperature of the stomach is about 100° Fahrenheit.
42. That the temperature is not elevated by the ingestion of food.
43. That exercise elevates the temperature; and that sleep or rest, in a recumbent position, depresses it.
44. That gentle exercise facilitates the digestion of food.
45. That the time required for that purpose is various, depending upon the quantity and quality of the food, state of the stomach, &c.; but that the time ordinarily required for the disposal of a moderate meal of the fibrous parts of meat, with bread, &c.; is from three to three and a half hours.
A few more inferences are given, but are here omitted because they refer exclusively to the chyle, which has not yet been treated of. The first is probably erroneous, and the second and seventeenth are, perhaps, too strongly expressed. A complete change of diet, for example, causes some variation in the gastric juice, although the latter inference, taken in a literal sense, affirms the contrary.
CHAPTER IV.
CHYLIFICATION, AND THE ORGANS CONCERNED IN IT.
Chylification—Not well known.—Organs concerned in it.—The intestinal canal—Its general structure.—Peritoneal coat—Mesentery—Muscular coat—Uses of these.—Air in intestines—Uses of.—Mucous coat—Analogous to skin—The seat of excretion and absorption—Mucous glands—Absorbent vessels—Course of chyle towards the heart.—Nerves of mucous coat.—Action of bowels explained.—Individual structure of intestines—The Duodenum—Jejunum—and Ileum.—Liver and pancreas concerned in chylification—Their situation and uses.—Bile, its origin and uses.—The pancreas—Its juice—The jejunum described—The ileum—Cœcum—Colon—and Rectum.—Peristaltic motion of bowels—Aids to it.—Digestion of vegetables begins in stomach but often finished in the bowels.—Illustration from the horse—Confirmation by Dupuytren.
The conversion of food into chyme, an operation which, as we have seen, takes place in the stomach, is only one of the series of changes which aliment undergoes before becoming fit to be assimilated with the living body; and the next process which we have to notice is chylification, or that by which chyme is converted into chyle.
In proportion as chyme is formed from the food, it is gradually propelled, as already shewn, through the pyloric orifice of the stomach into the duodenum or beginning of the small intestine. On its arrival there, it is acted upon by the bile from the liver, and the pancreatic juice from the pancreas; and the result is the separation of the chyme into two distinct substances,—the one a milky-white fluid called chyle, which is absorbed into the system, and forms nutriment,—and the other a yellowish and more consistent mass, which is the indigestible remains of the food, and which, after traversing the whole length of the intestinal canal, and being there mixed with the waste matter separated from the blood in order to be thrown out of the system through the same channel, is at last expelled in the form of fæces or excrement.