Coffee may be considered a member of the general class of adjuvant, or auxiliary, foods to which other beverages and condiments of negligible inherent food value belong. Its position on the average menu may be attributed largely to its palatability and comforting effects. However, the medicinal value of coffee in the dietary and per se must not be overlooked.
The ingestion of coffee infusion is always followed by evidences of stimulation. It acts upon the nervous system as a powerful cerebro-spinal stimulant, increasing mental activity and quickening the power of perception, thus making the thoughts more precise and clear, and intellectual work easier without any evident subsequent depression. The muscles are caused to contract more vigorously, increasing their working power without there being any secondary reaction leading to a diminished capacity for work. Its action upon the circulation is somewhat antagonistic; for while it tends to increase the rate of the heart by acting directly on the heart muscle, it tends to decrease it by stimulating the inhibitory center in the medulla.
The effect on the kidneys is more marked, the diuretic effect being shown by an increase in water, soluble solids, and of uric acid directly attributable to the caffein content of the coffee taken. In the alimentary tract coffee seems to stimulate the oxyntic cells and slightly to increase the secretion of hydrochloric acid, as well as to favor intestinal peristalsis. It is difficult to accept reports of coffee accomplishing both a decrease in metabolism and an increase in body heat; but if the production of heat by the demethylation of caffeine to form uric acid and a possible repression of perspiration by coffee be considered, the simultaneous occurrence of these two physiological reactions may be credited.
The disagreement of medical authorities over the physiological effects of coffee is quite pronounced. It will be noticed that the majority opinion is that coffee in moderation is not harmful. Just how much coffee a person may drink, and still remain within the limits of moderation and temperance, is dependent solely upon the individual constitution, and should be decided from personal experience rather than by accepting an arbitrary standard set by some one who professes to be an authority on the matter.