Digestion is a purely mechanical operation and the digestive apparatus, may be considered as a winnowing mill, the effect of which is, to extract all that is nutritious and to get rid of the chaff.
The manner in which digestion is effcted has been so long a question for argument, and persons have sought to ascertain if it were effected by coction, fermentation, solution, chemical, or vital action.
All of these modes have their influence, and the only error was that many causes were sought to be attributed to one.
In fact food impregnated by all fluids which fill the mouth and oesophagus, reaches the stomach where it is impregnated by the gastric juices, which always fill it. It is then subjected for several hours to a heat of 30 [degrees] Reaumer; it is mingled by the organic motion of the stomach, which their presence excites. They act on each other by the effect of this juxtaposition and fermentation must take place. All that is nourishing ferments.
In consequence of all of these operations, chyle is elaborated and spread over the food, which then passes the pylorus and enters the intestines. Portion after portion succeeds until the stomach is empty, thus evacuating itself as it was filled.
The pylorus is a kind of chamber between the stomach and the intestines, so constructed that food once in it can ascend only with great difficulty. This viscera is sometimes obstructed when the sufferer, after long and intense agony, dies of hunger.
The next intestine beyond the pylorus is the duodenum. It is so called because it is twelve fingers long.
When chyle reaches the duodenum, it receives a new elaboration by being mingled with bile and the panchreatic juice. It loses the grey color and acidity it previously possessed, becomes yellow and commences to assume a stercoral odor, which increases as it advances to the rectum. The various substances act reciprocally on each other; there must, consequently, be many analagous gasses produced.
The impulse which ejected chyle from the stomach, continues and forces the food towards the lower intestines, there the chyle separates itself and is absorbed by organs intended for the purpose, whence it proceeds to the liver, to mingle with the blood, which it revives, and thus repairs the losses of the vital organs and of transpiration.
It is difficult to explain how chyle, which is a light and almost insipid fluid, can be extracted from a mass, the color of which, and the taste, are so deeply pronounced.