The classical description given by Dr. Beaumont, that there was a movement of the gastric contents from the cardia along the greater curvature to the pylorus, and then back again along the lesser curvature, is no longer tenable since the researches of Cannon on living animals. By means of the fluoroscope and the X-rays he has established the fact that the fundus acts as a reservoir, slowly pressing its contents through a ring or muscular band - the transverse band or sphincter of the pyloric antrum - between it and the pyloric portion of the stomach. The part of the fundus nearest the pylorus converts this tonic constriction into waves passing towards the pyloric portion at regular intervals of fifteen to twenty seconds. When the liquefied food reaches the pyloric side of the transverse band, it is carried forwards by the running waves and then by contraction of the muscular walls pushed backwards to the afore-mentioned ring.

The mixing takes place entirely in the pyloric portion of the stomach, the contents of which are never commingled with those in the fundus. Indeed, the mass of food in this latter part of the stomach remains in layers, which arrange themselves in accordance with the order in which the items of the meal are swallowed. For this reason, salivary digestion is able to be carried on until the secretion of the hydrochloric acid penetrates the mass sufficiently to neutralise the alkaline saliva. This ensues in the space of three-quarters of an hour, or it may be as long as two hours, and then proteolysis begins slowly to take place.

It is contended that carbohydrates should be eaten at the beginning of a meal, for by this means free hydrochloric acid will appear rapidly, because there is no protein to combine with it. Now, as free hydrochloric acid is the mechanism causing the pylorus to relax, the stomach contents will in such case be much more quickly expelled into the duodenum, leaving the subsequent protein food to be more efficaciously dealt with in the absence of starches. When the contractions in the pyloric portion of the stomach have produced a thorough mixing of the food with the secretion, and when the necessary free hydrochloric acid has developed, the pylorus relaxes and the acid contents are propelled into the duodenum. The pylorus then contracts, and the alkaline secretions of the pancreas, intestine, and liver neutralise the acid chyme ejected from the stomach. When this is completed, the pylorus again relaxes, and this procedure goes on automatically under the influence of reflex action, until the stomach is emptied and in normal cases becomes microscopically clean. By this arrangement the acid stomach and alkaline intestine are kept from injuring each other.

When this description of gastric digestion was first published, physiologists hailed it with delight, and accepted it literally, but further experimentation and reflection have presented some difficulties, so that later observers are not inclined to accept the statement without reservation. At any rate, different interpretations are put upon the appearances as seen through the fluorescent screen, and this is hardly to be wondered at when we remember the difficulties associated with all X-ray diagnosis. It is rather startling at first, in examining with this apparatus a person in the erect posture, to notice that the apparently normal stomach is situated much lower down in the abdomen than we were taught to expect to find it. It would not be surprising if we are compelled to change our views on this matter also. Amongst others, Hutchison has pointed out that whilst the presence of free HC1 seems to increase the activity of the movements, these are able to take place quite efficiently when no gastric juice is secreted at all, as in cases of achylia. Then he mentions several reasons why the presence of free HC1 in the stomach should not be looked upon as the mechanism for causing relaxation of the pylorus, amongst them the fact that in cases of gastric fistula excess of acid may cause pyloric spasm, and, at all events, free HC1 in these cases tends to inhibit the opening of the pylorus. These are not altogether conclusive reasons for rejecting the new view, as the conditions in disease need not necessarily be similar to those in health.

Besides, there is no doubt that the pylorus exercises a certain amount of discrimination before deciding to relax and permit the exit of its contents. The passage of fluid takes place early, in jets of a few c.c. four times a minute, and is hardly ever delayed. Hard substances and indigestible masses are not only rejected by a tightening of the pylorus, but carried back by a reflex current, and this causes a delay in the exit of softer food as well.

Carbohydrates begin to leave the stomach within fifteen minutes, and with such rapidity that they are all expelled within three hours. Fats pass out much less freely, although less than half an hour elapses before they begin to enter the duodenum, but at the end of six hours much of the meal still remains in the stomach. Proteins never leave the stomach before the end of half an hour, although in six hours they have usually all been ejected. Proteins delay the exit of carbohydrates, while fats exert a deterrent influence on the escape of both proteins and carbohydrates. Probably the order of procedure is controlled by the stage when liquefaction or digestion is effected by the gastric juices.

In fasting animals and in certain digestive disturbances, the pylorus may open to allow a reflux of digestive juices from the intestines. Excess of fatty acids, e.g., when too much fat is given with the food, and excess of hydrochloric acid passing into the duodenum, causes a free secretion of bile, pancreatic fluid, and succus entericus. Neutralisation follows, the pylorus opens, and the fluids pass into the stomach.