The secretion of hydrochloric acid is only temporarily increased, after which its secretion is diminished, while the alcohol hinders the formation of pepsin. It also causes the mucous glands to pour such large quantities of alkaline fluid (mucus) into the stomach that this upsets gastric digestion.

It has been definitely established that tea and coffee both retard gastric digestion. Coffee is considered to have less effect than tea, providing they are both of the same strength. Since, however, coffee is customarily used in a stronger infusion than is tea, the effects of coffee in actual practice are about the same as those of tea. Their inhibiting effects are largely due to their modifying influence on the chemical processes of digestion.

The effects of these two poisonous infusions do not end with retarding the processes of digestion. They affect the stomach itself. Tea in particular, rich in tannic acid, and other astringent agents, acts as a strong irritant to the lining membrane of the stomach. Caffeol, and other substances produced by the roasting of coffee, are greater irritants even than tea. Chronic gastric catarrh and other disorders of the stomach may easily be produced and maintained by the effects of these two popular drinks.

Aside from these effects upon the stomach and the effects upon the nervous system and kidneys, produced by these two drugs, they undoubtedly affect the intestine and colon as well. There are many people upon whom coffee produces a laxative effect and this indicates that its irritating effects extend to the intestine and colon. Perhaps they also retard intestinal digestion.

As de-caffeinized coffee is not decaffeinized, and since, if it were, the coffee would still possess its tannic acid, caffeol and other poisons, and would in addition to its other effects, continue to retard digestion and injure stomach and kidneys, there seems to be no rational excuse for continuing its use.

In the well-known experiments upon Saint Martin it was found that a piece of metal could be introduced into the stomach but it would not occasion any flow of gastric juice. If, however, someone entered the room with a platter of steaming steak, the instant the man's eyes fell upon this the gastric juice would begin to flow into the stomach. When no gastric juice was needed none was supplied. Pavlov, introduced into the stomach of a sleeping dog (through a fistula) 100 grams of flesh. After an hour and a half the flesh was withdrawn by means of a string that had been tied to the meat. The loss to the meat was only six grams. This same amount of meat (100 grams) was again introduced into the stomach through the fistula, after the dog had been allowed to see and smell the meat. Under these conditions the weight of the meat was reduced by 30 grams in the same time. The reader will readily perceive the importance of such facts in diet. They teach us that food must be seen, smelled and tasted if digestion is to proceed normally. But the food must not be so disguised by condiments, spices, etc., as to deceive the senses as this will hinder the setting into motion, through the nerves, of the mechanism necessary to digestion.

The flow of gastric juice into the stomach is apparently in advance of the actual arrival of food and seems to be proportioned to the pleasure afforded by eating. This should teach us that the pleasure we derive from eating is only a means to an end, not the end itself.

The secretion of gastric juice is hastened and retarded by a number of factors the chief of which are here given:

Accelerated by	Retarded by:
(1) Hunger	(1) Fear, worry, anxiety, anger and other destructive emotions
(2) Pleasurable taste	(2) Failure to taste food
(3) Sight and smell of food	(3) Absence of hunger
(4) Thought of food	(4) Lack of proper salivary digestion
(5) Joy, happiness, etc.	(5) Pain, fever, etc.
(6) Effects of food on lining of stomach
(7) Ingestion of water
(8) Secretagogues arising as by-products of the process of digestion

Pepsin, the protein-splitting enzyme of the gastric juice, converts proteins into peptones. Beyond coagulating the casein of milk, renin appears to have no other function. Gastric lipase has but little effect upon fats.

Pavlov, the renowned Russian physiologist, has shown (see his The Work of the Digestive Glands) that the first secreted portions of the gastric juice are not always stronger in digestive power than that secreted an hour or so later. The strongest juice is poured out when it is most needed--when the quantity of food is large and when its structure is coarse. His experiments have proved that each kind of food calls forth a particular activity of the digestive glands and that the powers of the juice vary with the quantity of the feeding. Khizhin, one of his co-workers, performed experiments which have shown that feeding mixed diets, or separated administrations of milk, bread and meat, calls forth each time special modifications in the activity of the gastric glands. The secretion response is not "limited to the powers of the juice but extends to the rate of its flow, and also its total quantity." This proves that the character of the food not only determines the digestive power of the gastric juice, but also its total acidity. The acidity is greatest with meat and least with bread.

Prof. Pavlov says: "On proteid in the form of bread, five times more pepsin is poured out than on the same quantity of protein in the form of milk, and that flesh nitrogen requires more pepsin than that of milk. These different kinds of proteids receive, therefore, quantities of ferment corresponding to the differences in their digestibility."

Comparing equivalent weights, Pavlov found that flesh requires the most and milk the least amount of gastric juice;but comparing equivalents of nitrogen, he found that bread needs the most and flesh the least juice. The gland work per hour is almost the same with milk and flesh diets, but far less with bread. The last, however, exceeds all the others in the time required for its digestion, and consequently, the flow of juice is somewhat prolonged.

"Each separate kind of food," he says, "determines a definite hourly rate of secretion and produces characteristic limitations in the powers of the juices. Thus with a fish diet, the maximum rate of secretion occurs during the first and second hour, and the quantity of juice in each being approximately the same. With a broad diet, we have invariably a pronounced maximum in the second hour; and with milk a similar one during the second and third hours."

The acidity of gastric juice is determined by the food eaten, by the length of time that has elapsed since the food was consumed, and by the familiarity or unfamiliarity of the system with the food. Physicians persistently ignore these facts in making gastric tests and in feeding in hyper- and hypo-acidity. They invariably feed foods in hyper-acidity that increase the acidity and feed foods in hypo-acidity that decrease acidity. They make the same mistakes with regard to pepsin, for what is true of hydrochloric acid is true also of the secretion of pepsin.

"On the other hand," says Pavlov, "the most active juice occurs with flesh in the first hour; with bread in the second and third; and with milk in the last hour of secretion. Thus the period of maximum outflow, as well as the whole curve of secretion, is characteristic for each diet."

Pavlov also says: "The work of the gastric glands, in providing juice for the different food stuffs, must be recognized to be also purposive in another sense. The vegetable protein of bread requires for its digestion much ferment. This demand is supplied less by an increase in the volume of the juice than by and extraordinary concentration of the fluid poured out. One may infer from this that it is only the ferment of the gastric juice that is here in great requisition, and that large quantities of hydrochloric acid would be useless, or possibly injurious. We see from the following, that during gastric digestion of bread, an excess of hydrochloric acid is actually avoided. The total quantity of juice secreted on bread is only a little larger than that secreted on milk. It is distributed, however, over a much longer time, so that the mean hourly curve of juice with the bread diet is one and one-half times less than after taking milk or flesh. Consequently, in the digestion of bread but little hydrochloric acid is present in the stomach during the period of secretion. This harmonizes well with the facts of physiologic chemistry, namely, that the digestion of starch is impeded by an excess of acid.

"From clinical observation, we know further that, in cases of hyperacidity, a large part of the starch of bread escapes unused from the gastro-intestinal canal, while the flesh is excellently digested."

Are we not fully justified, by these facts, in assuming that the variations observed in gland activity during the course of digestion have some essential meaning? Each kind of food produces a special curve of secretion, and there must be a definite purpose for it, and a special significance to the secretory reaction. Pavlov holds that the work of the digestive glands, while elastic, is at the same time specific, precise and purposive. These facts are useful in working out proper food combinations, as we shall see later.

There are foods, like the starches, which, so far as stomach digestion is concerned, can only be digested in an alkaline medium--saliva--and others, like the proteins, which can only be digested in an acid medium--gastric juice--and if eaten together, interfere with the digestion of each other. We are justified in calling these incompatible foods.

From these facts it becomes obvious that the digestion of carbohydrates and of proteins is quite different. Indeed they are almost incompatible, for the requirements of each are so different that, when taken together, one forestalls the proper gastric digestion of the other. Another important observation should be taken into consideration at this point. Carbohydrates, proteins and fats are always mixed in the diet of most people. Fats have no stimulating effect on the gastric glands; whether the oil or fat is consumed before a meal, during the meal, or after the meal, an inhibitory influence upon gastric secretion becomes apparent immediately. If consumed after the meal and the gastric juice has begun to flow, it exerts an inhibitory influence which lasts usually for one or two hours.

Fat depresses, or inhibits, the normal activity of the secretory processes and this inhibitory effect while, perhaps partly mechanical, is for the most part chemical, as is shown by the results of administering milk with an increased amount of fat. The amount of juice secreted upon cream is less in amount and weaker in power than the small amount of weak juice poured out upon milk.

Nor is the effect of fat on the secretion of gastric juice limited to the depression of the flow of the gastric juice. Its preventive influence may last from one-half to two hours; only to be followed in the third hour, if the meal of fat be at all large, by a renewed secretion of gastric juice. This late secretion is much prolonged and furnishes a considerable quantity of gastric juice and it seems to be an explanation for many cases of hyperacidity which follow the taking of oils, butter fats and meat fats with a protein meal.

Bile precipitates pepsin, so that its presence in the stomach stops protein digestion even though the contents of the stomach remain acid. (Fasting is indicated in such cases). Trypsin (pancreatic) digests pepsin so that its action does not long continue in the intestine. Bile also stops its action, as does alkalinity.