Page:Popular Science Monthly Volume 15.djvu/360

 property is that of converting starch into grape-sugar." According to Wundt, "the mouth secretions possess, besides mechanical, chiefly a chemical action—the changing over of the starch and glycogen contained in the food into sugar. The ferment body, which produces this transformation, ptyaline, is not a specific element of the mouth-secretion, since, aside from the intestinal secretions, all tissues and fluids of the body contain starch-ferment."

From this it will be seen that no digestive action on meat or animal food takes place before reaching the stomach, and that, for vegetable food even, the action of the mouth-secretions is far from all-important.

As to the mechanical action of the mouth in preparing the food for deglutition, this is not specially necessary for morsels of meat of the ordinary size introduced into the mouth, while for a large portion of the vegetable or plant products eaten—and it is upon these that the saliva exerts its chemical action—mastication is necessary before they can be swallowed. The meat-foods are in themselves sufficiently moist, while many dried fruits, breads, and the like, in endless variety, first need thorough reduction.

A piece of jelly the size of a walnut would give little trouble in swallowing, since it is moist and of a yielding character, while few can swallow a pill the size of a pea without distress. Teeth and chewing, then, have their purpose, but, with the exception of the incisors occasionally, that purpose does not include meat unless it has become dried; this is with respect to the food before it reaches the stomach, but, of course, the question then arises, Would it not be in a better condition for digestion if it had been thoroughly masticated?

The food on reaching the stomach is kept in rotary motion by the muscular walls, and only after a time does it begin to pass the pyloric orifice, and then only by degrees, since the digestion farther on is a much finer operation, and can go on but slowly. The length of time that the digestion properly takes, is, according to the present knowledge of the subject, several hours—in fact, somewhat longer than has generally been supposed. Now, if the meat is swallowed fine cut, it begins to pass through very quickly, and before it has been fully acted upon by the gastric juice. This action as regards meats consists in "dissolving the sarcolemma from the muscular fibers, and in dissolving proteid matters and converting them into peptones. . . . On starch, gastric juice has per se no effect whatever. . . . On grape-sugar and cane-sugar healthy gastric juice has no effect." In fats alone it has a slight emulsifying effect, but if still in the tissue it is dissolved out. Milk is accordingly acted on by being first curdled on reaching the stomach, after which it is leisurely dissolved again in the desired form.

The rotary movement of the contents of the stomach is to facilitate the action of the gastric juice—to bring the various particles and