This section is from "Scientific American Supplement". Also available from Amazon: Scientific American Reference Book.
[Footnote: From a lecture delivered at the Sanitary Congress, at Newcastle-on-Tyne, September 28, 1882.]
By PROF. DE CHAUMONT, F.R.S.
Although eating cannot be said to be in any way a new fashion, it has nevertheless been reserved for modern times, and indeed we may say the present generation, to get a fairly clear idea of the way in which food is really utilized for the work of our bodily frame. We must not, however, plume ourselves too much upon our superior knowledge, for inklings of the truth, more or less dim, have been had through all ages, and we are now stepping into the inheritance of times gone by, using the long and painful experience of our predecessors as the stepping-stone to our more accurate knowledge of the present time. In this, as in many other things, we are to some extent in the position of a dwarf on the shoulders of a giant; the dwarf may, indeed, see further than the giant; but he remains a dwarf, and the giant a giant.
The question has been much discussed as to what the original food of man was, and some people have made it a subject of excited contention. The most reasonable conclusion is that man is naturally a frugivorous or fruit-eating animal, like his cousins the monkeys, whom he still so much resembles. This forms a further argument in favor of his being originated in warm regions, where fruits of all kinds were plentiful. It is pretty clear that the resort to animal food, whether the result of the pressure of want from failure of vegetable products, or a mere taste and a desire for change and more appetizing food, is one that took place many ages ago, probably in the earliest anthropoid, if not in the latest pithecoid stage. No doubt some advantage was recognized in the more rapid digestion and the comparative ease with which the hunter or fisher could obtain food, instead of waiting for the ripening of fruits in countries which had more or less prolonged periods of cold and inclement weather. Some anatomical changes have doubtless resulted from the practice, but they are not of sufficiently marked character to found much argument upon; all that we can say being that the digestive apparatus in man seems well adapted for digesting any food that is capable of yielding nutriment, and that even when an entire change is made in the mode of feeding, the adaptability of the human system shows itself in a more or less rapid accommodation to the altered circumstances.
Food, then, is 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 those functions directly, controls, directs, or assists their performance. With this wide definition it is evident that we include all the ordinary articles recognized commonly as food, and that we reject all substances recognized commonly as poisons. But it will also include such substances as water and air, both of which are essential for nutrition, but are not usually recognized as belonging to the list of food substances in the ordinary sense. When we carry our investigation further, we find that the organic substances may be again divided into two distinct classes, namely, that which contains nitrogen (the casein), and those that do not (the butter and sugar).
On ascertaining this, we are immediately struck with the remarkable fact that all the tissues and fluids of the body, muscles (or flesh), bone, blood--all, in short, except the fat--contain nitrogen, and, consequently, for their building up in the young, and for their repair and renewal in the adult, nitrogen is absolutely required. We therefore reasonably infer that the nitrogenous substance is necessary for this purpose. Experiment has borne this out, for men who have been compelled to live without nitrogenous food by dire necessity, and criminals on whom the experiment has been tried, have all perished sooner or later in consequence. When nitrogenous substances are used in the body, they are, of course, broken up and oxidized, or perhaps we ought to say more accurately, they take the place of the tissues of the body which wear away and are carried off by oxidation and other chemical changes.
Now, modern science tell us that such changes are accompanied with manifestations of energy in some form or other, most frequently in that of heat, and we must look, therefore, upon nitrogenous food as contributing to the energy of the body in addition to its other functions.
What are the substances which we may class as nitrogenous. In the first place, we have the typical example of the purest form in albumin, or white of egg; and from this the name is now given to the class of albuminates. The animal albuminates are: Albumin from eggs, fibrin from muscles, or flesh, myosin, or synronin, also from animals, casein (or cheesy matter) from milk, and the nitrogenous substances from blood. In the vegetable kingdom, we have glutin, or vegetable fibrin, which is the nourishing constituent of wheat, barley, oats, etc.; and legumin, or vegetable casein, which is the peculiar substance found in peas and beans. The other organic constituents--viz., the fats and the starches and sugars--contain no nitrogen, and were at one time thought to be concerned in producing animal heat.
We now know--thanks to the labors of Joule, Lyon Playfair, Clausius, Tyndall, Helmholtz, etc.--that heat itself is a mode of motion, a form of convertible energy, which can be made to do useful or productive work, and be expressed in terms of actual work done. Modern experiment shows that all our energy is derived from that of food, and, in particular from the non-nitrogenous part of it, that is, the fat, starch, and sugar. The nutrition of man is best maintained when he is provided with a due admixture of all the four classes of aliment which we have mentioned, and not only that, but he is also better off if he has a variety of each class. Thus he may and ought to have albumen, fibrine, gluten, and casein among the albuminates, or at least two of them; butter and lard, or suet, or oil among the fats; starch of wheat, potato, rice, peas, etc., and cane-sugar, and milk-sugar among the carbo-hydrates. The salts cannot be replaced, so far as we know. Life may be maintained in fair vigor for some time on albuminates only, but this is done at the expense of the tissues, especially the fat of the body, and the end must soon come; with fat and carbo hydrates alone vigor may also be maintained for some time, at the expense of the tissues also, but the limit is a near one, In either of these cases we suppose sufficient water and salts to be provided.
We must now inquire into the quantities of food necessary; and this necessitates a little consideration of the way in which the work of the body is carried on. We must look upon the human body exactly as a machine; like an engine with which we are all so familiar. A certain amount of work requires to be done, say, a certain number of miles of distance to be traversed; we know that to do this a certain number of pounds, or hundredweights, or tons of coal must be put into the fire of the boiler in order to furnish the requisite amount of energy through the medium of steam. This amount of fuel must bear a certain proportion to the work, and also to the velocity with which it is done, so both quantity and time have to be accounted for.
No lecture on diet would be complete without a reference to the vexed question of alcohol. I am no teetotal advocate, and I repudiate the rubbish too often spouted from teetotal platforms, talk that is, perhaps, inseparable from the advocacy of a cause that imports a good deal of enthusiasm. I am at one, however, in recognizing the evils of excess, and would gladly hail their diminution. But I believe that alcohol properly used may be a comfort and a blessing, just as I know that improperly used it becomes a bane and a curse. But we are now concerned with it as an article of diet in relation to useful work, and it may be well to call attention markedly to the fact that its use in this way is very limited. The experiments of the late Dr. Parkes, made in our laboratory, at Netley, were conclusive on the point, that beyond an amount that would be represented by about one and a half to two pints of beer, alcohol no longer provided any convertible energy, and that, therefore, to take it in the belief that it did do so is an error. It may give a momentary stimulus in considerable doses, but this is invariably followed by a corresponding depression, and it is a maxim now generally followed, especially on service, never to give it before or during work.
There are, of course, some persons who are better without it altogether, and so all moderation ought to be commended, if not enjoyed.
There are other beverages which are more useful than the alcoholic, as restoratives, and for support in fatigue. Tea and coffee are particularly good. Another excellent restorative is a weak solution of Liebig's extract of meat, which has a remarkable power of removing fatigue. Perhaps one of the most useful and most easily obtainable is weak oatmeal gruel, either hot or cold. With regard to tobacco, it also has some value in lessening fatigue in those who are able to take it, but it may easily be carried to excess. Of it we may say, as of alcohol, that in moderation it seems harmless, and even useful to some extent, but, in excess, it is rank poison.
There is one other point which I must refer to, and which is especially interesting to a great seaport like this. This is the question of scurvy--a question of vital importance to a maritime nation. A paper lately issued by Mr. Thomas Gray, of the Board of Trade, discloses the regrettable fact that since 1873 there has been a serious falling off, the outbreaks of scurvy having again increased until they reached ninety-nine in 1881. This, Mr. Gray seems to think, is due to a neglect of varied food scales; but it may also very probably have arisen from the neglect of the regulation about lime-juice, either as to issue or quality, or both. But it is also a fact of very great importance that mere monotony of diet has a most serious effect upon health; variety of food is not merely a pandering to gourmandism or greed, but a real sanitary benefit, aiding digestion and assimilation. Our Board of Trade has nothing to do with the food scales of ships, but Mr. Gray hints that the Legislature will have to interfere unless shipowners look to it themselves.
The ease with which preserved foods of all kinds can be obtained and carried now removes the last shadow of an excuse for backwardness in this matter, and in particular the provision of a large supply of potatoes, both fresh and dried, ought to be an unceasing care; this is done on board American ships, and to this is doubtless owing in a great part the healthiness of their crews. Scurvy in the present day is a disgrace to shipowners and masters; and if public opinion is insufficient to protect the seamen, the legislature will undoubtedly step in and do so.
And now let me close by pointing out that the study of this commonplace matter of eating and drinking opens out to us the conception of the grand unity of nature; since we see that the body of man differs in no way essentially from other natural combinations, but is subject to the same universal physical laws, in which there is no blindness, no variableness, no mere chance, and disobedience of which is followed as surely by retribution as even the keenest eschatologist might desire.