The food does not fall down this tube into the stomach, for the simple reason that the gullet is not wide open like the windpipe; each part is only open when the food is going down, and it is opened by the food, for as soon as it gets to one part, that part contracts upon it, and, as it were, squeezes it to the next, and so on; and this peristaltic action does not merely happen with food, but with drink also. When you take drink into your mouth and swallow it, it does not fall down the gullet; it is swallowed in precisely the same manner as the solid food, and that is illustrated by the fact that when a horse drinks the drink cannot fall up his neck into his stomach, he swallows it up his neck. We need not go to horses; there are some persons who can stand on their heads, and drink while standing on their heads; it is a common feat of jugglers.

When a man drinks standing on his head, it is quite clear that the water does not fall up his neck; so that whether eating or drinking we deliberately swallow the thing almost in morsels, at any rate in portions.

While we are using our mouths we know what we are about, for all the apparatus connected with our mouths is a voluntary apparatus. The instant food has got into the pharynx and is going down the gullet, we have nothing whatever more to do with it; the movements which go on in the gullet are purely involuntary; we can only directly influence our action upon the food that is in our mouths - and that is a very important point to consider in this way - that it points out to us that these actions in our mouths, resulting in the subdivision of the food and its mixture with the saliva, are voluntary actions, and that we ought not to be doing anything else at the same time; our attention ought not to be occupied with other things while we are masticating the food in our mouths, or the result is, that the food is not sufficiently divided, not sufficiently mixed with the saliva, and therefore not properly digested, and if not properly digested it cannot be absorbed, and so does not conduce to the nourishment of the body.

I have told you that the food is mixed in the mouth with the saliva. This exerts an important chemical action upon it in the following way. There is a great deal of cooked starch in our food. Now the saliva has the property of turning starch which cannot be absorbed into the blood at all, into a particular form of sugar, which is very readily absorbed into the blood. Besides having a mechanical use, the saliva has then also the chemical use of beginning the process of digestion, by changing one part of the food which is in a form in which it cannot be absorbed into the blood and into the body, into another form, namely a kind of sugar, which can most readily be absorbed into the body. This mixture of food and saliva passes down the gullet, in the way I have described, into the bag we call the stomach. Now, the stomach is situated across the upper part of the abdomen, rather more on the left side than on the Tight; the gullet or swallow comes into it nearly, but not quite, at its left end.

The coats of the stomach are similar to those of the gullet, only that the fibrous coating on the outside of the stomach is continuous with the serous bag which is wrapped about the outside of all the organs in the abdomen; that bag is called the peritoneum, because it is round about the intestines. You will understand what I mean, when I tell you that the bag is folded about outside of the organs, in a similar, though more complicated maimer, to that in which the serous bag, the pericardium, is folded around the heart, and . the two serous bags, the pleura, are folded around the lungs.

Then in the mucous membrane of the stomach, just as in the mucous membrane of the mouth, there are certain depressions which we call glands.

In the first place, there are a large number of comparatively simple depressions, which are chiefly situated at the left end of the stomach, which goes by the name of the cardiac end, because it is below the heart. These depressions secrete a fluid called mucus, and so go by the name of mucous glands.

Besides that, there are in the stomach some long deep depressions, tubular glands, which secrete a special kind of fluid. This fluid, because it is secreted in the stomach, goes by the name of gastric juice, and the glands are called gastric glands. This juice is an acid liquid, capable of dissolving certain important parts of the food (parts which I shall mention more particularly when I come to speak of foods), viz. the fleshy parts, and of reducing them to a condition in which they are capable of being absorbed into the blood. The gastric juice, you will notice, is poured out by glands, which are situated at the end of the stomach, at which the food goes out. And so you see that even in our stomachs, one part of the stomach does not do precisely the same thing as another, and you have thus shadowed out the idea of the complex stomachs of certain animals which have foods very difficult to digest. For instance, cows and sheep have several stomachs, i.e. their stomach has several distinct compartments, and in each certain things are done. We have one, but still, at the same time, different parts of it have different kinds of glands, which secrete different kinds of fluids for different purposes.