An elaborate investigation of the action of tea and coffee on digestion in the stomach was made by Fraser,[222] in which he found that both retard peptic digestion, the former to a greater degree than the latter. The digestion of white of egg, ham, salt beef, and roast beef was much less affected than that of lamb, fowl, or bread. Coffee seemed actually to aid the digestion of egg and ham. He attributed the retarding effect to the tannic acid of the tea and the volatile constituents of the coffee--the caffein itself favoring digestion rather than otherwise. Tea increased the production of gas in all but salt foods, whereas coffee did not. Coffee is, therefore, to be preferred in cases of flatulent dyspepsia. Hutchinson, in his _Food and Dietetics_, opines: As regards the practical inferences to be drawn from experiences and observations, it may be said that in health the disturbance of digestion produced by the infused beverages (tea and coffee) is negligible. Roberts, indeed, goes so far as to suggest that the slight slowing of digestion which they produce may be favored rather than otherwise, as tending to compensate for too rapid digestibility which refinements of manufacture and preparation have made characteristic of modern foods. Regarding increase in secretory activity, Moore and Allanston[223] report that in their experience meat extracts, tea, caffein solution, and coffee call forth a greater gastric secretion than does water, while with milk the flow of gastric juice seems to be retarded. Cushing[224] and others support this statement. This action is partially explained by Voit on the grounds that all tasty foods increase gastric secretion, the action being partly psychological; but Cushing observed the same effects upon introducing coffee directly into the stomachs of animals. In general, a moderate amount of coffee stimulates appetite, improves digestion and relieves the sense of plenitude in the stomach. It increases intestinal peristalsis, acts as a mild laxative, and slightly stimulates secretion of bile. Excessive use, however, profoundly disturbs digestive function, and promotes constipation and hemorrhoids.[225] There is much evidence to support the view that "neither tea, coffee, nor chicory in dilute solutions has any deleterious action on the digestive ferments, although in strong solutions such an action may be manifest."[226] After conducting exhaustive experiments with various types of coffee, Lehmann[227] concluded that ordinary coffee is without effect on the digestion of the majority of sound persons, and may be used with impunity. _Coffee in the Dietary--Food Value_ There are three things to be considered in deciding upon the inclusion of a substance in the dietary--palatability, digestibility without toxicity or disarrangement, and calorific value. Coffee is as satisfactory from these viewpoints as any other food product.