Both the external temperature and the internal body heat influence digestive processes. The effect upon the system of the temperature of food and drink is also a matter of important consideration.

Hot food and drinks in cold weather, cold food and beverages in hot weather, are instinctively resorted to by almost every one, although this is, no doubt, as much due to mental association and, perhaps, a temporary agreeable sensation of the temperature in swallowing as it is to any decided influence exerted over the body temperature.

Sudden modifications in the external temperature of either excessive heat or cold react upon the circulation, respiration, and the nervous system in a variety of ways and indirectly affect the digestive apparatus. The shock of sudden or, more particularly, of continued exposure to cold over the entire surface of the body tends to constrict the peripheral blood vessels and produce congestion of the visceral vessels, modifying secretion and absorption in consequence. A local application of heat and of cold over the abdominal wall during activity of the digestive organs has but limited influence. Patients wearing a Leiter coil over the abdomen through which ice water is continually passed for many hours do not necessarily suffer from retarded digestion, nor do those who are having poultices continuously applied to the abdomen. In a series of experiments which I have made to determine the extent of heat penetration through the abdominal wall it has been shown that the application of heat or of cold of such extremes as can be borne without discomfort has little or no influence on the circulation in the stomach or the intestines or upon the temperature of those organs so long as the subcutaneous circulation is vigorous.

This is owing to the rapid neutralisation of the heat or cold applied externally by the constantly changing layer of blood flowing beneath the surface. In dogs, a poultice of 1400 F. or an ice coil with water at 340 F. placed over one side of the abdominal wall does not raise the temperature of a long-stemmed thermometer more than a quarter of a degree when slipped beneath the abdominal wall through a perforation or held immediately below the poultice or coil. If, however, the animal be killed, circulation ceases, and the temperature of the thermometer will immediately be affected to the extent of fifteen or twenty degrees. It is doubtful, therefore, whether enfeebled digestion can be much influenced by the local application of warmth over the abdominal wall. Many persons, however, who have a tendency to intestinal indigestion find it both agreeable and salutary to wear continuously a broad flannel bandage about the abdomen to favour uniformity in temperature and prevent the liability of taking cold.

It is incompatible with life that the variations of body temperature between the highest fever and the lowest depression should exceed the limits of temperature at which digestion is known to proceed when artificially conducted, so that these alterations do not of themselves alone destroy digestive power in the stomach. The latter is usually diminished or lost during fever, but this may be owing more to disturbances of the circulatory and nervous systems than to increased warmth of the stomach.

Efforts to raise or lower the local temperature in the stomach during digestion by swallowing, respectively, hot water or pounded ice are not productive of very striking results.

It is customary, and no doubt best, to administer stimulants hot in collapse from any cause.

Wunderlich, Fothergill, and others have laid considerable stress upon the antipyretic value of giving all fluids very cold in fevers, but I have yet to see any effect upon genuine pyrexia, as, for example, in typhoid fever, depending upon whether milk or other fluids were administered very hot or iced. I often prescribe hot boiled milk in such cases if patients prefer it, because the quantity of heat units which can be thus conveyed into the body is too small to merit serious consideration.

It is a popular belief that rich wines and oils are heating" foods, and, conversely, "cooling drinks" have long been used in fevers, but the use of iced fluids and of cracked ice itself for relief of thirst in fevers is of comparatively recent date. It followed the extended introduction of the clinical thermometer, and to this day one occasionally meets with opposition from mothers to giving a child with high fever anything really cold.

Hot fluids drunk also favour perspiration, and sometimes aid expectoration, but this is because they are promptly absorbed and added to the volume of the blood, not because they contribute many heat units to the body. Winternitz endeavoured to show by sphyg-mograms that the imbibition of cold fluids increases arterial tension, and that of hot fluids lessens it. This may be true, but the sphyg-mograph is not at all a reliable instrument, and certainly the clinical application of this rule is not capable of substantiation, although in giving hot-air baths to promote perspiration in Bright's disease hot drinks are of undoubted service.

With practice one may learn to swallow water which is uncomfortably hot to the touch - at a temperature of 115° or 1200 F. It has been swallowed at even 1320 F. The drinking of very hot water before meals aids in cleansing the mucous membrane in. cases of gastric catarrh and acts as a diuretic. The rate of local digestion in the stomach is comparatively little influenced by swallowing either hot fluids, such as soups or broths, or hot solid foods, and similarly it is not much retarded by taking such substances very cold, provided in each case they are swallowed very slowly. Some food is more digestible when eaten hot than cold, but with other food the reverse is true. In either case it is not so much because of the warming or cooling of the stomach, but because of the physical condition of the food. For example, some persons who cannot digest hot mutton fat can take it cold because it becomes friable and mixes better with other food. Some persons with very sensitive stomachs cannot take the fat of cold butter spread upon bread, but can digest it if melted thoroughly into hot toast, which subdivides the fat particles and keeps them from fusion. Hot boiled ham is more indigestible than cold ham for many persons.

Hot milk may be more digestible for invalids than iced milk, yet the latter may be better borne if vomiting be present. Much must depend upon habit and individual peculiarities. One may begin a dinner with iced raw oysters, then take hot soup, and later conclude the meal with ice cream, followed by hot coffee, and yet throughout, the temperature of the stomach contents does not vary so much as half a degree, because the warm blood circulating so rapidly and abundantly within its walls and those of the oesophagus maintains the necessary normal average most favourable to digestion. Hot food is cooled and cold food is warmed in swallowing, and it may be said the hotter or the colder it is, the less likely it is to modify the rate of gastric digestion, for these extremes of temperature necessitate slow swallowing. Swallowing several tumblerfuls of iced water in quick succession does cool the stomach and inhibit digestion by local reduction of temperature, and also by shock to the gastric nerves; but even this effect is less than is commonly supposed.

There are about fourteen pounds of blood in the body, having an average temperature of very nearly 100° F., all of which in turn keeps circulating through the digestive organs, and a single tumblerful of iced water poured into such a volume of warm fluid would not lower the temperature of the whole very much. This is why swallowing pounded ice is of so little avail to control gastric haemorrhage, and much less pulmonary haemorrhage, although it may relieve nausea somewhat. In support of these statements are the results of many experiments which I have made upon patients undergoing treatment by lavage, to whom I have given fluids at different temperatures, which were immediately siphoned out of the stomach, and tested for heat loss or gain. Two tumblerfuls of ice water may be slowly swallowed, and if siphoned out again in five minutes the temperature of the fluid will be found to have risen to fully 950 F.

The question has often been raised as to whether the body temperature can be permanently affected by alterations in the quality of the diet. It may be definitely stated that so long as the diet is abundant and nutritious it makes no difference whether man is carnivorous, a vegetarian, or lives upon mixed diet. Insufficient food and starvation or inanition from improper food, it is well known, reduce the body temperature to from one to three or more degrees below normal. Excess of alcohol also reduces it.

Improper and indigestible food may cause temporary rise in temperature, but this is usually caused by more or less gastritis or gastro-enteritis, and is therefore independent of normal considerations. The total daily variation in body temperature normally produced by the ingestion of food does not commonly exceed ° F., but it may reach 1° F. The vegetarian rabbit has as high a temperature as a dog fed upon animal food alone. The grass-eating cow has a temperature two or three degrees above man's and quite equal to that of many strictly carnivorous animals. The graminivorous pigeon has a temperature as high as that of the fish-eating gull. No deductions can therefore be made in regard to any permanent influence of diet upon normal body temperature in healthy animals or in man.

The loss of body heat consequent upon starvation and inanition will be discussed under those headings.