Chapter XIX The Physiology of Nutrition
I have repeatedly spoken of the nitrogenous and non-nitrogenous constituents of food, assuming that the nitrogenous are the more nutritious, are the plastic or flesh-building materials, and that the non-nitrogenous materials cannot build up flesh or bone or nervous matter, can only supply the material of fat, and by their combustion maintain the animal heat.
In doing so I have been treading on loose ground—I may say on a scientific quicksand. When I first taught practical physiology to children in Edinburgh, many years ago, this part of the subject was much easier to teach than now. The simple and elegant theory of Liebig was then generally accepted, and appeared quite sound.
According to this, every muscular effort is performed at the expense of muscular tissue; every mental effort, at the expense of cerebral tissue; and so on with all the forces of life. This consumption or degradation of tissue demands continual supplies of food for its renewal, and as all the working organs of the animal are composed of nitrogenous tissue, it is clearly necessary, according to this, that we should be supplied with nitrogenous food to renew them, seeing that the nitrogen of the air cannot be assimilated by animals at all.
But besides doing mechanical and mental work, the animal body is continually giving out heat, and its temperature must be maintained. Food is also demanded for this, and the non-nitrogenous food is the most readily combustible, especially the hydro-carbons or fats; the carbo-hydrates—starch, sugar, &c.—also, but in lower degree. These, then, were described as fuel food, or heat-producers.
This view is strongly confirmed by a multitude of familiar facts. Men, horses, and other animals cannot do continuous hard work without a supply of nitrogenous food; the harder the work the more they require, and the greater becomes their craving for it. On the other hand, when such food is eaten in large quantities by idle people, they become victims of inflammatory disease, or their health otherwise suffers, according, probably, to whether they assimilate or reject it.
Man is a cosmopolitan animal, and the variations of his natural demand for food in different climates affords very direct support to Liebig’s theory. Enormous quantities of hydro-carbon, in the form of fat, are consumed by the Esquimaux and by Europeans when they winter in the Arctic regions. They cannot live there without it. In hot climates some fuel food is required, and the milder form of carbo-hydrates is chosen, and found to be most suitable; rice, which is mainly composed of starch, is an example. Sugar also. Offer an Esquimaux a tallow candle and a rice or tapioca pudding; he will reject the latter, and eat the former with great relish.
A multitude of other facts might be stated, all supporting Liebig’s theory.
There is one that just occurs to me as I write, which I will state, as it appears to have been hitherto unnoticed. Some organs which act in such wise that we can see their mode of action are visibly disintegrated and consumed by their own activity, and may be seen to demand the perpetual renewal described by Liebig. There are glands of cellular structure which cast off their terminal cells containing the fluid they secrete; do their work by giving up their own structural substance at their peripheral working surface.
Where, then, is the quicksand? It is here. If muscular and mental work were done at the expense of the nitrogenous muscular and cerebral tissues, the quantity of nitrogen excreted should vary with the amount of work done. This was formerly stated to be the case without hesitation, as the following passage from Carpenter’s ‘Manual of Physiology’ (3rd edition, 1856, page 256), shows: ‘Every action of the nervous and muscular systems involves the death and decay of a certain amount of the living tissue, as is indicated by the appearance of the products of that decay in the excretions.’
More recent experiments by Fick and Wislicenus, Parkes, Houghton, Ranke, Voit, Flint, and others are said to contradict this by showing that the waste nitrogen varies with the quantity of nitrogenous food that is eaten, but not with the muscular work done. For the details of these experiments I must refer the reader to standard modern physiological treatises, as a full description of them would carry me too far away from my immediate subject. (Dr. Pavy’s ‘Treatise on Food’ has an introductory chapter on ‘The Dynamic Relations of Food,’ in which this subject is clearly treated in sufficient detail for popular reading.)
It is quite the fashion now to rely upon these later experiments; but for my own part, I am by no means satisfied with them—and for this reason, that the excretions from the skin and from the lungs were not examined.
It is just these which are greatly increased by exercise, and their normal quantity is very large, especially those from the skin, which are threefold, viz. the insensible perspiration, which is transpired by the skin as invisible vapour; the sweat, which is liquid, and the solid particles of exuded cuticle.
Lavoisier and Seguin long ago made very laborious experiments upon themselves in order to determine the amount of the insensible perspiration. Seguin enclosed himself in a bag of glazed taffeta, which was tied over him with no other opening than a hole corresponding to his mouth; the edges of this hole were glued to his lips with a mixture of turpentine and pitch. He carefully weighed himself and the bag before and after his enclosure therein. His own loss of weight being partly from the lungs and partly from the skin, the amount gained by the bag represented the quantity of the latter; the difference between this and the loss of his own weight gave the amount exhaled from the lungs.
He thus found that the largest quantity of insensible exhalation from the lungs and skin together amounted to 3½ oz. per hour, or at the rate of 5¼ lbs. per day. The smallest quantity was 1 lb. 14 oz., and the mean was 3 lbs. 11 oz. Three-fourths of this was cutaneous.
These figures only show the quantity of insensible perspiration during repose. Valentin found that his hourly loss by cutaneous exhalation while sitting amounted to 32·8 grammes, or rather less than 1¼ oz. On taking exercise, with an empty stomach, in the sun, the hourly loss increased to 89·3 grammes, or nearly three times as much. After a meal followed by violent exercise, with the temperature of the air at 72° F., it amounted to 132·7 grammes, or nearly 4½ times as much as during repose. A robust man, taking violent exercise in hot weather, may give off as much as 5 lbs. in an hour.
The third excretion from the skin, the epithelial or superficial scales of the epidermis, is small in weight, but it is solid, and of similar composition to gelatin. It should be understood that this increases largely with exercise. The practice of sponging and ‘rubbing down’ of athletes removes the excess; but I am not aware of any attempt that has been made to determine accurately the quantity thus removed.
Does the skin excrete nitrogenous matter that may be, like urea, a product of the degradation or destruction of muscular tissue?
The following passage from Lehmann’s ‘Physiological Chemistry’ (vol. ii. p. 389), shows that the skin throws out plenty of nitrogen obtained from somewhere: ‘It has been shown by the experiments of Milly, Jurine, Ingenhouss, Spallanzani, Abernethy, Barruel, and Collard di Martigny, that gases, and especially carbonic acid and nitrogen, are likewise exhaled with the liquid secretion of the sudiparious glands. According to the last-named experimentalist the ratio between these two gases is very variable; thus, in the gas developed after vegetable food there is a preponderance of carbonic acid, and, after animal food, there is an excess of nitrogen. Abernethy found that on an average the collective gas contained rather more than two-thirds of carbonic acid and rather less than one-third of nitrogen.’ But it appears that less gas is exhaled when there is much liquid perspiration.
Lehmann’s summary of the experiments of Abernethy, Brunner, and Valentin (vol. ii. p. 391), gives the amount of hourly exudation, under ordinary circumstances, as 50·71 grammes of water, 0·25 of a gramme of carbon, and 0·92 of a gramme of nitrogen. This amounts to 21½ grammes of nitrogen per day in the insensible perspiration; three-quarters of an ounce avoirdupois, or as much nitrogen as is contained in one pound and a half of natural living muscle.
That the liquid perspiration contains compounds of nitrogen, and just such compounds as would result from the degradation of nitrogenous tissue, is unquestionable. As Lehmann says (vol. ii. p. 389), ‘the sweat very easily decomposes, and gives rise to the secondary formation of ammonia.’ Simon and Berzelius found salts of ammonia in the sweat: that the ammonia is combined both with hydrochloric acid and with organic acids: that it probably exists as carbonate of ammonia in alkaline sweat.
The existence of urea in sweat appears to be uncertain; some chemists assert its presence, others deny it. Favre and Schottin, for example, who have both studied the subject very carefully, are at direct variance. I suspect that both are right, as its presence or absence is variable, and appears to depend on the condition of the subject of the experiment.
Favre describes a special nitrogenous acid which he discovered in sweat, and names it hydrotic or sudoric acid. Its composition corresponds, according to his analysis, to the formula C10H8NO13.
I have summarised these facts, as they show clearly enough that conclusions based on an examination of the quantity of nitrogen excreted by the kidneys alone (and such is the sole basis of the modern theories), are of little or no value in determining whether or not muscular work is accompanied with degradation of muscular tissue. The well known fact that the total quantity of excretory work done by the skin increases with muscular work, while that from the kidneys rather diminishes, indicates in the plainest possible manner that an examination of the skin secretion should be primary in connection with this question. To entirely neglect this in such a research is a scientific parallel to the histrionic feat of performing the tragedy of ‘Hamlet’ with the Prince of Denmark omitted.
Seeing that it has been entirely neglected, I am justified in expressing, very plainly and positively, my opinion of the worthlessness of all the modern research upon which the alleged refutation of Liebig’s theory of the destruction and renewal of living tissue in the performance of vital work is based, and my rejection of the modern alternative hypothesis concerning the manner in which food supplies the material demanded for muscular and mental work.
I may be accused of rashness and presumption in thus attempting to stem the overwhelming current of modern scientific progress. Such, however, is not the case. It is modern scientific fashion, rather than scientific progress, that I oppose. We have too much of this millinery spirit in the scientific world just now; too much eagerness to run after ‘the last thing out,’ and assume, with undue readiness, that the ‘latest researches’ are, of course, the best—especially where fashionable physicians are concerned.
Having summarised Liebig’s theory of the source of vital power, and its supposed refutation by modern experiments, I will now endeavour to state the alternative modern hypothesis, though not without difficulty, nor with satisfactory result, seeing that the recent theorists are vague and self-contradictory. All agree that vital power or liberated force is obtained at the expense of some kind of chemical action of a destructive or oxidising character, and is, therefore, theoretically analogous to the source of power in a steam-engine; but when they come to the practical question of the demand for working fuel or food, they abandon this analogy.
Pavy says (‘Treatise on Food and Dietetics,’ page 6): ‘In the liberation of actual force, a complete analogy may be traced between the animal system and a steam-engine. Both are media for the conversion of latent into actual force. In the animal system, combustible material is supplied under the form of the various kinds of food, and oxygen is taken in for the process of respiration. From the chemical energy due to the combination of these, force is liberated in an active state; and, besides manifesting itself as heat, and in other ways peculiar to the animal system, is capable of performing mechanical work.’ In another place (page 59 of same work), after describing Liebig’s view, Dr. Pavy says: ‘The facts which have been already adduced’ (those above described on the nitrogen eliminated by the kidneys), ‘suffice to refute this doctrine. Indeed, it may be considered as abundantly proved that food does not require to become organised tissue before it can be rendered available for force-production.’ On page 81 he says: ‘While nitrogenous matter may be regarded as forming the essential basis of structures possessing active or living properties, the non-nitrogenous principles may be looked upon as supplying the source of power. The one may be spoken of as holding the position of the instrument of action, while the other supplies the motive power. Nitrogenous alimentary matter may, it is true, by oxidation contribute to the generation of the moving force, but, as has been explained, in fulfilling this office there is evidence before us to show that it is split up into two distinct portions, one containing the nitrogen, which is eliminated as useless, and a residuary non-nitrogenous portion which is retained and utilised in force-production.’
The italics are mine, for reasons presently to be explained. Pavy’s work contains repetitions and further illustrations of this attribution of the origin of force to the non-nitrogenous elements of food.
Then we have a statement of the experiments of Joule on the mechanical equivalent of heat, connected with experiments of Frankland with the apparatus that is used for determining the calorific value of coal, &c.—viz. a little tubular furnace charged with a mixture of the combustible to be tested, and chlorate of potash. This being placed in a tube, open below, and thrust under water, is fired, and gives out all its heat to the surrounding liquid, the rise of temperature of which measures the calorific value of the substance (see fig. 7, page 21, ‘Simple Treatise on Heat’).
From this result is calculated the mechanical work obtainable from a given quantity of different food materials. That from a gramme is given as follows:
| Beef fat | 27,778 | —Units of work, or number of pounds lifted one foot. | |
| Starch (arrowroot) | 11,983 | ||
| Lump sugar | 10,254 | ||
| Grape sugar | 10,038 |
In Dr. Edward Smith’s treatise on ‘Food,’ the foot-pound equivalent of each kind of food is specifically stated in such a manner as to lead the student to conclude that this represents its actual working efficiency as food. Other modern writers represent it in like manner.
Here, then, comes the bearing of these theories on my subject. A practical dietary or menu is demanded, say, for navvies or for athletes in full work; another for sedentary people doing little work of any kind.
According to the new theory, the best possible food for the first class is fat, butter being superior to lean beef in the proportion of 14,421 to 2,829 (Smith), and beef fat having nearly eight times the value of lean beef. Ten grains of rice give 7,454 foot-pounds of working-power, while the same quantity of lean beef gives only 2,829; according to which 1 lb. of rice should supply as much support to hard workers as 2½ lbs. of beefsteak. None of the modern theorists dare to be consistent when dealing with such direct practical applications.
I might quote a multitude of other palpable inconsistencies of the theory, which is so slippery that it cannot be firmly grasped. Thus, Dr. Pavy (page 403), immediately after describing bacon fat as ‘the most efficient kind of force-producing material,’ and stating that ‘the non-nitrogenous alimentary principles appear to possess a higher dietetic value than the nitrogenous,’ tells us that ‘the performance of work may be looked upon as necessitating a proportionate supply of nitrogenous alimentary matter,’ and his reason for this admission being that such nitrogenous material is required for the nutrition of the muscles themselves.
A pretty tissue of inconsistencies is thus supplied! Non-nitrogenous food is the best force-producer—it corresponds to the fuel of the steam-engine; the nitrogenous is necessary only to repair the machine. Nevertheless, when force production is specially demanded, the food required is not the force-producer, but the special builder of muscles, the which muscles, according to theory, are not used up and renewed in doing the work.
It must be remembered that the whole of this modern theoretical fabric is built upon the experiments which are supposed to show that there is no more elimination of nitrogenous matter during hard work than during rest. Yet we are told that ‘the performance of work may be looked upon as necessitating a proportionate supply of nitrogenous alimentary matter,’ and that such material ‘is split up into two distinct portions, one containing the nitrogen, which is eliminated as useless.’ This thesis is proved by experiments showing (as asserted) that such elimination is not so proportioned.
In short, the modern theory presents us with the following pretty paradox. The consumption of nitrogenous food is proportionate to work done. The elimination of nitrogen is not proportionate to work done. The elimination of nitrogen is proportionate to the consumption of nitrogenous food.
I have tried hard to obtain a rational physiological view of the modern theory. When its advocates compare our food to the fuel of an engine, and maintain that its combustion directly supplies the moving power, what do they mean?
They cannot suppose that the food is thus oxidised as food, yet such is implied. The work cannot be done in the stomach, nor in the intestinal canal, nor in the mesenteric glands, nor in their outlet, the thoracic duct. After leaving this, the food becomes organised living material, the blood being such. The question, therefore, as between the new theory and that of Liebig, must be whether work is effected by the combustion of the blood itself or by the degradation of the working tissues, which are fed and renewed by the blood. Although this is so obviously the only rational physiological question, I have not found it thus stated.
Such being the case, the supposed analogy to the steam-engine breaks down altogether; the food is certainly assimilated, is converted into the living material of the animal itself before it does any work, and therefore it must be the wear and tear of the machine itself which supplies the working power, and not that of the food as mere fuel material shovelled directly into the animal furnace.
I thus agree with Playfair, who says that the modern theory involves a ‘false analogy of the animal body to a steam-engine,’ and that ‘incessant transformation of the acting parts of the animal machine forms the condition for its action, while in the case of the steam-engine it is the transformation of fuel external to the machine which causes it to move.’ Pavy says that ‘Dr. Playfair, in these utterances, must be regarded as writing behind the time.’ He may be behind as regards the fashion, but I think he is in advance as regards the truth.
My readers, therefore, need not be ashamed of clinging to the old-fashioned belief that their own bodies are alive throughout, and perform all the operations of working, feeling, thinking, &c., by virtue of their own inherent self-contained vitality, and that in doing this they consume their own substance, which has to be perpetually replaced by new material, its quality depending upon the manner of working and the matter and manner of replacement.
The course of our own evolution thus depends upon ourselves; we may, according to our own daily conduct, be building up a better body and a better mind, or one that shall be worse than the fair promise of the original germ. Therefore the philosophy of the preparation of the material of which the body and brain are built up and renewed must be worthy of careful study. This philosophy is ‘The Chemistry of Cookery.’
Footnotes
1 In applying heat to glass vessels, thickness is a source of weakness or liability to fracture, on account of the unequal expansion of the two sides, due to inequality of temperature, which, of course, increases with the thickness of the glass. Besides this, the thickness increases the leverage of the breaking strain.
2 Tarchnoff has recently discovered the curious fact that the white of the eggs of birds that are hatched without feathers remains transparent when coagulated, while the eggs which produce chickens and other birds already fledged become opaque when coagulated. This is familiarly illustrated by the difference between plovers’ eggs and hens’ eggs when cooked.
3 ‘Egg-cement,’ made by thickening white of egg with finely-powdered quicklime, has long been used for mending alabaster, marble, &c. For joining fragments of fossils and mineralogical specimens, it will be found very useful. White of egg alone may be used, if carefully heated afterwards.
4 Physiological Chemistry, vol. ii. p. 356.
5 It was given to me in 1868. I have just found that some of it remains unused (December 1884), and that it still retains its characteristic flavour.
6 The following, from Francatelli’s Modern Cook, is amusing, if not instructive: ‘Take two dozen garden snails, add to these the hind quarters only of two dozen stream frogs, previously skinned; bruise them together in a mortar, after which put them into a stewpan with a couple of turnips chopped small, a little salt, a quarter of an ounce of hay-saffron, and three pints of spring water. Stir these on the fire until the broth begins to boil, then skim it well and set it by the side of the fire to simmer for half an hour; after which it should be strained, by pressure through a tammy cloth, into a basin for use. This broth, from its soothing qualities, often counteracts, successfully, the straining effects of a severe cough, and alleviates, more than any other culinary preparation, the sufferings of the consumptive.’
7 Carpenter’s Manual of Physiology, 3rd edition, 1846, p. 267.
8 Londe, Nouveaux Éléments d’Hygiène, 2nd edition, vol. ii. p. 73.
9 The necessity for this is not so great as may appear theoretically. I have tried the experiment of having veal cutlets fried in a bath previously used for fish, and was not able to detect any fishy flavour as I expected I should. This was the case even when I knew that the fish fat had been used, and I was consequently far more critical than under ordinary circumstances. Even apple-fritters may be cooked in fat that has been used for fish. I have tried this since the above was written and am surprised at the result.
10 I have ventured to ascribe this lubricating function to the albumen which envelopes the fibres, though doubtful whether it is quite orthodox to do so. Its identity in composition with the synovial liquor of the joints, and the necessity for such lubricant, justify this supposition. It may act as a nutrient fluid at the same time.
11 I am greatly disgusted with the cookery-books, especially the pretentious volume of Francatelli’s, on being unable to find any recipe for this delicious Italian dish, and a similar absence of a dozen or two of equally common and excellent preparations familiar to all who have dined at the Lepre (Rome), or other good Italian restaurants.
12 Forty or fifty years ago these cheese fondus were one of the usual courses at many-course banquets, but now they are rarely found in the menu of such dinners. There is good reason for this. They are far too nutritious to be eaten with a dozen other things. Their proper use is to substitute the joint in an ordinary respectable meal of meat and pudding.
13 Before the Adulteration Act was passed, mustard flour was usually mixed with well-dried wheaten flour, whereby the redundant oil was absorbed, and the mixture was a dry powder. Now it is different, being pure powdered mustard seed, and usually rather damp. It not only lies closer, but is much stronger. Therefore, in following any recipe of old cookery-books, only about half the stated quantity should be used.
14 The reader who desires further information on this and kindred subjects will find it clearly and soundly treated (without any of the noxious pedantry that too commonly prevails in such treatises) in Dr. Andrew Combe’s Physiology of Digestion, which, although written by a dying man nearly half a century ago, still remains, like his Principles of Physiology, the best popular work on the subject. Subsequent editions have been edited and brought up to date by his nephew, Sir James Coxe.
15 In fairness to retailers I should state that the price of arrowroot just now is unusually low; the ordinary range is from twopence to two shillings. People who are afraid of having their arrowroot adulterated should ask themselves what can be used to cheapen the St. Vincent at the above-quoted prices, which are those of the unquestionably genuine article.
16 Shortly after the close of the Great Exhibition of 1851, when the South Kensington Museum was only in embryo, I had occasion to call on Dr. Lyon Playfair at the ‘boilers,’ and there found the Prince hard at work giving instructions for the arrangement and labelling of these analysed food products and the similarly displayed materials of industry, such as whalebone, ivory, &c. I then, by inquiry, learned how much time and labour he was devoting, not only to the general business of the collection, but also to its minor details.
17 Such lixivium is essentially a dilute solution of carbonate of potash in very crude form, not conveniently obtained by burners of pit coal. I tried the experiment of soaking some ordinary Indian corn in a solution of carbonate of potash, exceeding the ten or twelve hours specified by Count Rumford. The external coat was not removed even after two days’ soaking, but the corns were much swollen and softened. I suspect that this difference is due to the condition of the corn which is imported here. It is fully ripened, dried, and hardened, while that used by the Indians was probably fresh gathered, barely ripe, and much softer.
18 Ordinary tea contains about 2 per cent. of this. It may easily be obtained by making a strong infusion and slowly evaporating it to dryness, then placing this dried extract on a watch-glass or evaporating-dish, covering it with an inverted wineglass, tumbler, or conical cap of paper. A white fume rises and condenses on the cool cover in the form of minute colourless crystals. The tea itself may be used in the same manner as the dried extract, but the quantity of crystals will be less.
19 In repeating these experiments I find that the best form of silk is that which the Coventry dyers technically call ‘boiled silk,’ i.e. raw silk boiled in potash to remove its resinous varnish. In this state the aniline dyes attach themselves to the fibre very readily and firmly.
20 The following is from Knowledge of August 15, 1884. It is editorial, not mine, though I have heard these ‘Spirit Flavours’ spoken of by experts as ordinary merchandise. The Hungarian wine oil is one of them: ‘I have just obtained what is expressively known as “a wrinkle” from a wholesale price-list of a distiller which has fallen (no matter how) into my hands. That it was never intended to be seen by any mortal eyes outside of “the trade” goes without saying. In this highly instructive document I find, under the head of “Spirit Flavours,” “the attention of consumers in Australia and India” (we needn’t say anything about England) “is particularly called to these very useful and excellent flavours. One pound of either of these essences to fifty gallons of plain spirit” (let us suppose potato spirit) “will make immediately a fine brandy or old tom, &c., without the use of a still.—See Lancet report.” This is followed by a list of prices of these “flavours,” and then follows a similar one of “Wine Aromas.” A cheerful look-out all this presents, upon my word! The confiding traveller calls at his inn for some old brandy, and they make it in the bar while he is waiting. He orders a pint of claret or port, and straightway he is served with some that has been two and a half minutes in bottle! After the perusal of this price-list, I have come to the conclusion that in the case of no articles of consumption whatever is the motto Caveat emptor more needful to be attended to than in that of (so called) wines and spirits.’
21 Since the above was written I have met with some alarming revelations concerning the increasing prevalence of cancer, which, if confirmed, will force me to withdraw this conclusion. This horrible disease has increased in England with increase of prosperity—with increase of luxury in feeding—which in this country means more flesh food. In the ten years from 1850 to 1860, the deaths from cancer had increased by 2,000; from 1860 to 1870 the increase was 2,400; from 1870 to 1880 it reached 3,200, above the preceding ten years. The proportion of deaths is far higher among the well-to-do classes than among the poorer classes. It seems to be the one disease that increases with improved general sanitary conditions. The evidence is not yet complete, but as far as it goes it points most ominously to a direct connection between cancer and excessive flesh feeding among people of sedentary habits. The most abundant victims appear to be women who eat much meat and take but little out-of-door exercise.
22 I have lately learned that a patent was secured some years ago for ‘malt bread,’ and that such bread is obtainable from bakers who make it under a license from the patentee. The ‘revised formula’ for 1884, which I have just obtained, says: ‘Take of wheat meal 6 lbs., wheat flour 6 lbs., malt flour 6 oz., German yeast 2 oz., salt 2 oz., water sufficient. Make into dough (without first melting the malt), prove well, and bake in tins.’
When common sense and true sentiment supplant mere unreasoning prejudice, vegetable oils and vegetable fats will largely supplant those of animal origin in every element of our dietary.
It has been quoted in just that manner across numerous publications.
Page 109, “facts” changed to “fats” (the chemistry of fats)
Page 328, the text refers to the now more usually spelled “sauerkraut” as “sour-kraut” in the text and “Sauer-kraut” in the index. These usages were retained as printed.