Much has been written about the need of man changing his diet when he removes from one climate to another, in the belief that the natives always eat the kind of food best adapted to the climate in which they live. This is superficial reasoning, and too much importance is attached to the relations of climate to diet per se. As a matter of fact, the natives of a country eat what they can obtain easiest, or what their habits and mode of life have accustomed them to in the struggle for the survival of the fittest. " Climate affects diet mainly by the supply it affords" (Chambers).

"The national dietary is determined largely by the climate and nature of the available soil, and among civilised communities it is largely modified as facilities for commerce and interchange of food products are increased.

"Maritime people naturally derive much nitrogenous food from the sea, as fish, molluscs, crustaceans, etc. Among the residents of the far North albuminous and fatty diet predominates, and the coarser cereals - barley, rye, oats, etc. - being more hardy, predominate in their food. Barley grows the farthest north of all the cereals " (Clark).

The Hindu subsists mainly upon rice, one of the simplest types of farinaceous food, and he derives his nitrogen from corn and lentils. He must consequently eat a large bulk of food in order to obtain sufficient nitrogen for the needs of the system; his digestive organs enlarge, and he finds the means of stimulating them by the free use of condiments of various sorts. Bulky and fibrous vegetable food distends the alimentary canal. The natives of very hot countries live mainly upon vegetable and starchy foods, eating cereals, green vegetables, and pulpy fruits which contain water, salts, and acids in abundance, which are cooling and refreshing. As a rule, they eat less animal food than do the natives of temperate and arctic regions, nor do they require fats in excess, although they take some fats and oils.

While these statements apply to a majority of mankind, they are by no means without exception, and it must not be argued that because a tribe eats the only food which Nature has provided, they could not live equally well in their own climate upon other food, if they could obtain it. Far from depending solely upon vegetable food, most savage tribes living in the torrid zone eat meat ravenously when they can get it, and often prefer it in an advanced stage of decomposition.

The New Zealander and South Sea Islander choose a varied diet of fish, eggs, roots, seeds, berries, seaweeds, and meat if obtainable (see p. 32).

As pointed out by Chambers, the Pampas, who eat flesh and drink water only, thrive on hot arid plains, and so do the Nubian Arabs, while the peasants of northern Norway and southern Spain live alike almost wholly on breadstuffs without meat. He says that "the immediate transition from a purely animal to a purely vegetable diet, though borne by the individual, is fatal to the race," and "the best diet in the abstract is a mixed diet, and mixed in the proportion selected by the experience of most civilised nations, and it is also best for the individual who is accustomed to it to adhere to under whatever sky he may be wandering." In changing residence from one extreme of climate to another it is not advisable to alter the diet too suddenly, and more must depend upon the previous habits and occupation of the individual than upon external temperature. Meat eaters find it easier to adopt quickly another form of diet than vegetarians. The Dominican friars deteriorated so much in health in the British climate that they were obliged while resident in England to obtain special dispensation allowing them to eat meat four times a week.

The English soldiers transported to India or Africa are not required to become exclusive vegetarians; and the French in Africa or Panama have done best upon a mixed diet. In the United States Surgeon General's report for 1900 the statement is made that " experience in the Philippines has shown that though it is undoubtedly true that while leading quiet lives men eat less in a tropical climate than in a temperate or cold climate, and particularly of meat or fatty substances, our soldiers during the active operations of last year have shown no marked tendency to lessen the quantity of fresh meat eaten. Exhausting labours and fatigues with corresponding wear and tear of the muscular system require a liberal meat issue, which the soldier uses with satisfaction and advantage".

"Well-clad and sheltered soldiers require less rations than poorly clad men exposed to the weather - a good thing to know in times of great privation" (Woodruff).

Men often become involuntary vegetarians while travelling in hot climates from inability to procure meat, and may partially starve themselves from lack of appetite for monotonous food, variety being unobtainable. This leads them to resort to strong condiments, spices, curry, etc., to stimulate the appetite.

Many persons, especially those past middle life and people with a tendency to corpulency, find that during the heat of the summer season, and especially during the prevalence of " heat waves," they are in much better health when they abstain from hot soups, fat, and meat, and take but little animal food of any kind. The total quantity of food eaten may advantageously be reduced at this time of the year as much as one sixth, or even one fourth. Most persons find this out as a matter of individual experience; but there are others who should be especially directed in the matter, and the rule applies to infants as well as adults. The diet in winter should comprise both more nitrogen and more carbon than in summer.

The breakfast hour is often made half an hour or an hour earlier in summer than in winter to advantage.

The thirst engendered by living in hot climates is conducive to excessive drinking, and as the water is often bad, an additional excuse is often made for drinking too much liquor. By these means the foundations for hepatic and renal troubles, cirrhosis, and Bright's disease are often laid. On this account, in very hot climates strong alcoholic drinks ought especially to be avoided. In India they uniformly disagree, and lighter beverages, such as beer and wines, must be taken very sparingly; but there is no objection to tea, coffee, and chocolate.