As stated above, Mr. V. yields appetite gastric juice at: minimum secretion rate, 84 c.c. per hour; maximum secretion rate, 648 c.c. per hour; average secretion rate, 210 c.c. per hour. Does this furnish us a clew to the total gastric secretion on an average meal in man ? This question cannot be answered by direct measurements, even in cases of duodenal fistula and collection of all the chyme issuing through the pyloric opening, as the alimentary tract of such persons is far from normal, and we still have the variable factors of swallowed saliva and of direct absorption in the stomach.
In the case of dogs sham feeding alone may yield 600 to 700 c.c. of gastric juice in 4 to 6 hours. But this situation is abnormal because the sham feeding does not satisfy the appetite, even though the secretion inhibits the hunger. It is therefore certain that the appetite secretion is much less when the food is permitted to reach the stomach. But when the food is allowed to reach the stomach, how can we measure the total gastric secretion ? Using large dogs with fistula of duodenum, Moritz reports that the ingestion of 200 gm. of meat caused a secretion of 320 c.c. gastric juice in 7 hours. Part of this was undoubtedly swallowed saliva, and possibly some admixture of bile and pancreatic juice. With the same method Tobler obtained 200 to 300 c.c. of gastric juice from feeding 100 gm. meat; part of this fluid was undoubtedly swallowed saliva.
It seems to us that we can arrive at a very close estimate of the total average secretion of gastric juice in a man on the following basis: Pavlov and his pupils have shown on dogs that the secretion curves of the main and the accessory stomach pouch run parallel. They have also shown that on a meal of meat, or a mixed meal, the secretion usually reaches the maximum toward the end of the first or during the second hour. Lonnquist notes particularly that the secretion does not reach its maximum until toward the end of the second hour after eating. On the whole, the quantity of gastric juice yielded by a dog's accessory stomach after the first two hours following a moderate meal of meat, bread, or a mixture of meat and bread, is about half of that secreted during the entire digestion period. This is evident from experiments reported in detail by Pavlov and his students, as well as from studies on dogs in our laboratory. But this is not true if a very large quantity of food is given, or if the food contains a considerable amount of fat, as in both cases the secretion of fluid is greatly prolonged.
We can safely assume that the general relations and the relative importance of the appetite and the hormone gastric juice are the same in man and dog. Pflaunder supports the view that the maximum rate of secretion in man is reached at the end of the first or the beginning of the second hour of digestion. Sick finds that the maximum acidity of gastric content is usually reached at the end of the first hour of digestion. The same is shown by the more recent studies of Rehfus, Bergheim, and Hawk, using the Ewald rest meal on normal persons.
The total secretion of gastric juice in normal adult man on ingestion of the average dinner of meat, bread, vegetables, coffee or milk, and dessert will, on the foregoing assumptions, be as follows: 1st hour, 200 c.c. gastric juice; 2d hour, 150 c.c.; 3d to 5th hours, 350 c.c.; total, 700 c.c. gastric juice.
It should be noted in this connection that Mr. V.'s noonday meal is in reality the big meal or dinner. He secretes less gastric juice on his evening meal, probably not more than 400 to 500 c.c., and from the fact that he makes his breakfast solely on biscuits, coffee, and milk it is likely that his secretion of gastric juice on the morning meal does not exceed 250 to 300 c.c. This would make a total of 1,350 to 1,500 c.c. of gastric juice secreted in 24 hours. These figures do not include the continuous secretion in the absence of food. It is of interest to note that Pflaunder arrived at practically the same figures (1,500 c.c. or 25 c.c. per kg. of body weight in 24 hours), basing his estimate on calculations from the acidity and volume of the gastric content at varying periods after the meal.
It need not be pointed out that the foregoing figures are subject to great variations, depending on the condition of the stomach and the quality and quantity of the food.
The fluid contents of the "empty " stomach vary from nothing up to 150 c.c. The average of a number of tests varies with the individual from 30 to 50 c.c. The quantity is greater in the morning than at noon or at 6:00 p.m. It is on the whole greater in the summer than in the winter months. The most important factor in these daily and seasonal variations is probably the tonicity of the empty stomach and the rate of the continuous secretion.
The gastric glands in the normal person are never completely quiescent. The continuous secretion varies from 2 to 50 c.c. per hour. The higher figures are exceptional, but may obtain for several days in succession, again to revert to the lower figures.
The vagus secretory tonus is a possible and the auto-digestion of the gastric juice itself is a probable factor in this continuous gastric secretion. The secretion itself is rich in pepsin, but when the secretion rate is very low it is poor in free hydrochloric acid.
Chewing on indifferent substances and stimulation of the nerve-endings in the mouth by substances not related to food do not cause secretion of gastric juice, that is, these processes do not augment the continuous gastric secretion.
Seeing, smelling, and possibly thinking of palatable food usually cause a very slight and transitory secretion of gastric juice.
The rate of secretion of gastric juice on mastication of palatable food is directly proportional to the palatability of the food. During mastication the average rate is 3.5 c.c. per minute (minimum rate: 1.4 c.c.; maximum rate: 10.8 ex.). On cessation of chewing the secretion rate diminishes rapidly, so that in 15 to 20 minutes the gastric glands reach the level of the continuous gastric secretion. The chemistry of this appetite gastric juice is practically constant.
The latent period of this appetite secretion varies indirectly with the rate of the continuous secretion, so that when the continuous secretion is abundant the appetite secretion shows practically no latent period at all, while with the lowest rate of the continuous secretion the latent period varies from 2 to 3 minutes. This latent period is therefore one of the processes in the gland cells, and not in the nervous mechanism.
On the basis of these experiments on Mr. V., on the reports of other gastric fistula cases in man, and on the work of Pavlov on dogs, it is estimated that an adult normal" person secretes on an average meal (dinner) 700 c.c. of gastric juice, or an average total of 1,500 c.c. of gastric juice in 24 hours.
On the whole, this work on the appetite secretion of gastric juice in man confirms and extends the work of Pavlov and his pupils on dogs. Pavlov overlooked or ignored the continuous secretion in the absence of all food and psychic stimuli, and he put too great an emphasis on the secretion induced in a hungry animal by seeing and smelling food. The significant appetite secretion in man is that induced by tasting and chewing good food. The continuous secretion does not fit in with Pavlov's general theory of strict adoption of the digestion juices to the food, as it apparently serves no useful purpose in digestion.
It is also clear that Pavlov overestimated the importance of the appetite secretion in gastric digestion. The continuous secretion initiates gastric digestion in the absence of appetite juice. Dogs with both vagi sectioned exhibit practically normal gastric digestion within a few days after the operation, despite the fact that the appetite gastric juice is eliminated. Cats may be forcibly fed with unpalatable food and the stomach digestion is practically as rapid as when they eat voluntarily. And we know that in man the pepsin-hydrochloric acid of the gastric juice may be greatly reduced if not entirely absent (achylia) without marked impairment of gastric peristalsis or food utilization. We have on numerous occasions removed all the appetite gastric juice from Mr. Ws stomach before the masticated meal was put into his stomach without producing the slightest evidence of indigestion.
The significance of hunger and appetite for digestion is apparently not so much in the actual yield of appetite gastric juice as in the fact that when these sensation complexes are present the entire gastero-intestinal tract, both on the motor and on the secretory side, is in fit condition to handle the ingested food.