ART. III.-On the Relation of Food to Work. By J. HICKMAN, Army Medical Staff.

A FOOD may be defined to be any substance which can be taken into the body and applied to use, either in building up or repairing the tissues and framework of the body itself, or in providing energy and producing animal heat; or any substance which, without performing these functions directly, controls, directs, or assists their performance. It is clear that stress is to be laid upon the particular foods that provide the body with animal heat and potential energy, and that the other classes should be treated in their relation to these special duties.

There is no life without the potential energy of food being transformed into actual energy, shown under the various forms which constitute animal existence; there can be no such process of oxidation or source of power manifested without the continual renewal of the factors containing and supplying the force, and also the continual removal of the effete substances.

Food may be presented in the following classification for refer

ence:

Nitrogenous

Inorganic Non-nitrogenous

1. Albuminates, such as the animal albumens and vegetable glutens, which form the greater part of the solids of meat, fish, eggs, milk, and breadstuffs.

2. Fats (or hydrocarbons).-Animal and vegetable fats and oils.

3. Carbohydrates.-Farinaceous and saccharine compounds, such as starch, gum, sugar, glycogen, and inosite.

3a. Vegetable acids, changing into carbonates, and so preserving the alkalinity of the blood.

4. Salts (mineral) and water.

Now, to briefly enumerate the properties of the prominent members of this classification in respect to the subject of the

essay.

Albuminates.-As every tissue and fluid of the body contain

nitrogen, the presence of this element is essential to the growth and nutrition of the animal structures, without which energy could not be developed, and when developed is proportional to their activity. In the view of work it should not be forgotten that nitrogenous substances are broken up and carried away by oxidation, and the chemical changes must manifest themselves in energy, principally in the form of heat; so that this class directly contributes to force production. However, this would be an expensive source, and may be termed secondary, or unimportant. The chief use of nitrogenous food is to regulate the amount of oxygen required for the oxidation of the non-nitrogenous food; it is indispensable to the sufficient absorption of oxygen by the lungs and its utilisation in the system; part of it breaks up into a complementary unazotised portion which is applied to the development of force and the generation of heat. Voit and Pettenkofer maintain that fat is altogether formed from albuminates, and that carbohydrates, when accompanied by an abundant supply of albumen, cause fat to be separated and deposited from the albumen. Each quantity of albuminous food requires the presence of a corresponding quantity of carbohydrate to separate the amount of fat due to the former; 100 parts of water-free albumen yield 51-4 parts of fat. This estimate, and the general conclusions of Voit, must be taken in a guarded sense. Hoffmann's experiments and clinical observations seem to show that the ingested fats are stored up largely. The view of albuminates as a force-producer through their transformation into tissue fats could not be omitted from this discussion.

It thus seems that the proteids are burnt up directly and indirectly, and give rise to heat and mechanical work. The amount of energy evolved is, however, comparatively small, and to obtain sufficient for the requirement of work from proteids alone would mean the consumption of them in such quantities that the body would almost be poisoned with excess of nitrogen. If active exercise is taken, more oxygen is brought into the system, and the rapidity of the circulation is increased, and the surplus nitrogen is more easily excreted. What is arrived at is that the albuminates excite and increase the nitrogenous and non-nitrogenous meta

In muscle, or in the blood circulating through it, under ordinary circumstances, experiments seem sufficient to show that the non-nitrogenous substances, especially the fats, furnish the energy manifested as heat or muscular movement. But it is also probable that the nitrogenous substances also furnish a contingent of energy.

bolism, and that relatively the amount of them required varies with the exertion to be undergone.*

Fats.-There are different varieties of fat, differing in composition and their degrees of digestibility. In chemical composition they are non-nitrogenous-a large portion of the carbon and some of the hydrogen are readily oxidised. This oxidation is one of the chief sources of animal heat and other forms of force. In the table of relative values, in this respect, fat will be seen to be two and a half times more useful than starch. To the soldier, as well as to others called upon to undergo great bodily efforts and privations, fat proves itself indispensable. Chamois hunters, on their fatiguing chases, take no provisions rich in albumen only fat, and the 8 or 9 ozs. of bacon demanded for the German soldier in 1870 constitute an official recognition of the value of fat as an element in rational dietetics.

It must be remembered that the digestion of fat is limited, and if more than a certain quantity be given this model food simply passes through the system unchanged; indeed, fat is not easy of assimilation without plenty of exercise and a very active condition of the vital functions, and in tropical countries it must be somewhat sparingly consumed. An excess of fat (it is stated) lessens the absorption of oxygen, and consequently lessens oxidation of both fat and albuminates.b

* Experiments on the elimination of urea seem to demonstrate that there is a slight increase in the total excretion of nitrogen after exercise, and this probably in part proceeds from the disintegration of muscular tissue. But the relation of waste of the proper tissue of muscle to the amount of work is best compared to the trifling loss undergone by the framework of a machine whilst in action. The source of power or fuel is the carbohydrates and hydrocarbons of the food. Apart from this it seems certain that regular exercise produces in the muscular structure an addition of nitrogenous tissue. This and the preceding paragraph justify the necessity of increasing the nitrogen in any hard-working dietary. Also, during work the changes in the muscle consist in active oxidation. An increase in the supply of oxygen is a necessity for increased muscular action. As the absorption of oxygen has already been asserted to be dependent on the amount and vigour of the nitrogenous tissues, it follows if more oxygen is required more nitrogenous food is indicated.—(Voit and Pettenkofer.) b Exercise, or work, means a greater increase in the carbon excreted, and consequently an increase of carbon to be given in the food. This is, according to the teaching of physiology, best given in the form of fat, and not of starch, and this is supported by the natural instinct—preferring hydrocarbons when unusual exertion is demanded.

During hard work the appetite becomes keener, especially for meat and fat; the functions of digestion and absorption are more perfectly performed. This, too, points to the increase in any ration in these respects, and also in the salts—especially the chlorides and phosphates.

Carbohydrates comprise the sugars and starches, and form generally the greatest portion of all diets. They are valuable heat and force producers, like the fats, but only contain excess carbon, ready to combine with the oxygen of the blood; the hydrogen in them is already oxidised. Oxidation taking place most readily in them, if freely supplied they delay the metamorphosis of the nitrogenous and fatty tissues. This property of being easily disposed of by combination justifies a liberal use of the carbohydrates in the diet of hot countries.

The formation of fat indirectly promoted by the carbohydrates has been already mentioned; the direct production of fat from carbohydrates is now questioned." It is usually assumed by their deoxidation they are transformed into fat; and, as the sources of fat, the grand principle of the Banting diet is the avoidance of such articles of food, because in fats excess of carbohydrates lessens the supply of oxygen, and consequently the transformation of the other classes. Sugar is laid up as glycogen, which, perhaps, may be looked upon as a reserve of carbohydrate material, to be given up little by little, and taken up by the tissues. In many details there are striking differences between the fats and carbohydrates. On the other hand, it is safe to assert that the chief duty of the two groups is the production of force, and as such they could be classed together.

The other class of the carbohydrates, the vegetable acids, are useful in preserving health. They do not require notice in detail. The salts can be shown to be essential articles of diet; they may, however, influence the production of force, either by acting independently or by catalysis, in promoting oxidation in the body, and they are by some termed force-regulators. In this term, too, may be included condiments and accessory foods-tea, coffee, alcohol, &c.-which may certainly commence and increase chemical reactions. Whenever, then, increased energy is demanded, a considerable increase in salts must accompany the additional food.

In the preceding remarks heat and energy have been used together as convertible terms. This has been established by the labours of Joule and others. The law of the relation of heat and

"The action of carbohydrates resembles that of fat in protecting from metabolism a certain amount of the circulating albumen; and if given in excess they will, in consequence of the greater facility with which they undergo metabolism, lead to the more hardly metabolisable fat being left unchanged and deposited in the tissues. From this we may conclude that the generally assumed transformation of carbohydrates into fat does not take place.