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nor albumen will continue to be eaten by animals; they soon cease to eat it, and during the period in which it is taken they show unmistakable signs of starvation.
Albumen, then, is highly nutritious; and if we estimated the nutritive value of various articles according to their amounts of albumen, we should place caviare, ox-liver, and sweetbread at the top of the list, leaving the muscle of beef very far below them. The following table shows the proportions of albumen in 100 parts of various articles of food:
Fibrine is liquid in the serum of the blood, and is very closely allied to albumen-indeed, for a long while was supposed to be identical with it and with the fibrine of muscle, which is now more accurately called muscu line (by Lehmann syntonin). When the blood is drawn from the body, fibrine passes from the liquid to the solid state, and coagulates into what is called the clot, which is nothing but solid fibrine enclosing some of the red corpuscles. It was formerly supposed that this solidification was all that took place when blood fibrine passed into muscular fibre; but re
cent investigations have shown that muscle - fibrine is really a different substance, allied to, but not identical with blood-fibrine.
Albumen and fibrine are found abundantly in vegetables the former being most abundant in wheat, rye, barley, oats, maize, and rice. It is found also in the oily seeds, such as almonds, nuts, &c.; in the juices of carrots, turnips, cauliflowers, asparagus, &c.* Fibrine is also abundant in the cereals, grape-juice, and juice of other vegetables. Although closely allied to animal albumen and fibrine, they are not identical with these substances, differing from them both in composition and properties; but the differences are so slight, that vegetable albumen easily passes into animal albumen in the digestive pro
Caseine is another of the albuminous substances, and may be reinto which it readily passes. It forms garded as a modification of albumen, the curd, or coagulable matter of milk. Unlike albumen, it does not coaguvessel, an insoluble pellicle is formed late by heat. If heated in an open on the surface, as we often see in the milk-jug brought up with our coffee; but this effect is produced by the action of the oxygen of the atmosphere. The proportion of caseine in different kinds of milk is as follows:
* Albumen forms three compounds - basic, acid, and neutral. In the white of egg, and in the serum of blood, it is a basic albuminate of soda. In certain diseases it is a neutral albuminate in the blood.
version of the mother's blood into caseine, no elements of the constituents of blood have been separated. When chemically examined, caseine is found to contain a much larger proportion of the earth of bones than blood does, and that in a very soluble form, capable of reaching every part of the body. Thus, even in the earliest period of its life, the develop ment of the organs in which vitality resides is, in the carnivorous animal, dependent on the supply of a substance identical in organic composition with the chief constituents of its blood."* Caseine is found in beans, pease, lentils, almonds, nuts, and perhaps in all vegetable juices.
These three bodies albumen, fibrine, and caseine-are not inaptly designated "protein - bodies," even now that Mulder's idea of an organic radical, named by him " protein," has been generally given up. In the egg we see caseine arise from albumen, and in digestion caseine passes back again into albumen. Fibrine, again, appears to be only albumen with more oxygen; and it may be easily reconverted into albumen by nitrate of potash. It differs from albumen in assuming something of definite. structure when coagulated lating, which albumen never does. There are many unexplained facts known respecting fibrine, which, when explained, may clear away other obscurities. Lehmann found, by experiments on himself, that animal diet produced more fibrine in his blood than was produced by vegetable diet --a fact seemingly at variance with the fact that, during starvation, the quantity of fibrine is increased, as it is also during acute inflammations. Thus, animal diet, known to be nutritious, produces a result known to be characteristic of inflammation and starvation. Nor does the difficulty cease here: the blood of the vegetable feeders, among animals, has more fibrine than that of the fleshfeeders; yet the carnivorous dog has less fibrine when fed on vegetable food than when his diet has been exclusively animal. Finally, although
LIEBIG: Animal Chemistry, p. 52.
herbivora have more fibrine than carnivora, birds have more than both.
Gluten is not found in animals, but exists abundantly in vegetables, and is the most important of all the nitrogenous substances, because, as we have seen, it is capable of supporting life when given alone. "It is the presence of gluten in wheaten flour that renders it pre-eminently nutritious; and its viscidity or tenacity confers upon that species of flour its peculiar excellence for the manufacture of maccaroni, vermicelli, and similar pastes, which are made by a kind of wiredrawing, and for which the wheat of the south of Europe is peculiarly adapted."+ The following table, which is borrowed from Dr Pereira's work, gives the proportions of gluten in 100 parts of various vegetables :
Wheat, Middlesex (average crop), 19. 0 Spring
These four albuminoid substances, namely albumen, fibrine, caseine, and gluten, are remarkable among other things for their extreme instability, -the readiness with which they are transformed, or decomposed. It is this alterability which renders them peculiarly apt to act as ferments, and to induce chemical changes in the substances with which they come in contact. It is on this alterability that their great value in nutrition depends. Further, we must remark that, no matter what is the form in which they are eaten, whether as white of egg, fibrine, caseine, or gluten, they are all reduced by the digestive process to substances named
BRANDE'S Chemistry, quoted by PEREIRA. On this subject see the chapter "The Bread we Eat," in JOHNSTON'S Chemistry of Common Life.
peptones, under which forms only are they assimilable.
Gelatine. There is perhaps no substance on our list which more interestingly illustrates the want of a true scientific doctrine presiding over the investigations into Food than Gelatine: a substance richer in nitrogen than any of the albuminous substances, yet denied a place among the plastic elements: a substance which, under the forms of jellies and soups, is largely given to convalescents, who get strong upon it, yet which, we are emphatically assured, has no nutritive value whatever. Mulder says that no physician, who has had experience, could doubt the nutritive value of gelatine; and we may be pretty sure that common usage, in such cases, is founded upon some solid ground, and that no substance is largely used as food which has not a nutritive value. Common usage, or what is called " common sense," must not indeed be the arbiter of a scientific question; but it has a right to be heard, when it unequivocally contradicts the conclusions of Science; and it can only be put out of court on a clear exposition of the source of its error. In the present case, Science pretends that Gelatine cannot be nutritive, common sense asserts that it does nourish; and unless the fact can be proved against common sense, it will be reasonable to suppose that Science is arguing on false premises. False, indeed, are the premises, and false the conclusion. But let us see what has been the course of inquiry.
In 1682 the celebrated Papin discovered that bones contained organic matter, and he invented a method of extraction of this matter, which occupied the chemists and savans in the early days of the French Revolution with the laudable desire of furnishing food to the famished people. A pound of bones was said to yield as much broth as six pounds of beef, and, with the true fervour of inventors, the savans declared bone-soup to be better than meat-soup. In 1817, M. D. Arcet applied steam on a grand scale to the preparation of this gelatine from bones, promising to
make four oxen yield the alimentary value of five, as usually employed.
Great was the excitement, vast the preparations. In hospitals and poorhouses machines were erected which made an enormous quantity of Gelatine. Unfortunately the soup thus obtained was found far from nutritious; moreover, it occasioned thirst, digestive troubles, and finally diarrhoea. The savans heard this with equanimity. They were not the men to give up a theory on the bidding of vulgar experience. Diarrhoea was doubtless distressing, but science was not implicated in that. The fault must lie in the preparation of the soup; perhaps the fault was attributable to the soupeaters: one thing only was positive -that the fault was not in the Gelatine. In this high and unshaken confidence, the savans pursued their
Thousands of rations were daily distributed; but fortunately these rations were not confined to the bone-soup, or else the mortality would have been terrific. Few men of science had any doubts until M. Donné positively assured the Academy that experiments on himself, and on dogs, proved Gelatine, thus prepared, to be scarcely, if at all, nutritious. He found that employing a notable quantity in his own diet caused him rapidly to lose weight, and that during the whole experiment he was tormented with hunger and occasional faintness. A cup of chocolate and two rolls nourished him more effectually than two litres and a half of bone-soup accompanied by 80 to 100 grammes of bread.* These statements were confirmed by other experimenters, and the confidence in Gelatine was rudely shaken, and would have been ignominiously overthrown, had not Edwards and Balzac published their remarkable memoir (1833), in which experiments conducted with great care and scientific rigour established the fact that although Gelatine is insufficient to support life, it has nevertheless nutritive value. Dogs fed on gelatine and bread became gradually thinner and feebler; but when fed on bread alone, their loss was far more rapid.
A litre is a trifle more than a pint and a half; a gramme is about 15 grains.
At this period it became necessary to have the question definitively settled, and the French Academy appointed a Commission to report on it. This is the celebrated “Gelatine Commission" so often referred to. The report appeared in 1841. It showed that dogs perished from starvation in presence of the Gelatine extracted from bones, after having eaten of it only a few times. When, instead of this insipid Gelatine, the agreeable jelly which pork-butchers prepare from a decoction of different parts of the pig, was given them, they ate it with relish at first, then ceased, and died on the twentieth day, of inanition; when bread or meat, in small quantities, was given, the dogs lived a longer time, but grew gradually thinner, and all finally perished. A striking difference was observed between bone-soup and meat-soup: the animals starved on the first, and flourished on the second.
The conclusion generally drawn from this Report is, that Gelatine is not a nutritive substance. But all that is really proved by the experiments is that Gelatine alone is insufficient for nutrition; a conclusion which is equally true of albumen, fibrine, or any other single substance. For perfect nutrition there must be a mixture of inorganic and organic substances, salts, fats, sugars, and albuminates.
When animals are fed on albumen alone, or white of egg alone, with water as the single inorganic element, they perish; but they live perfectly well on raw bones and water-the reason being that bones contain salts and small proportions of albumen and fats to supplement the Gelatine, and they contain these in the state of organic combination, not in the state of chemical products. The paramount importance of this last condition may be gathered from the experiments mentioned in the Gelatine Report-namely, that boiling the bones, or digesting them in hydrochloric acid, and thus resolving their cartilaginous tissue into Gelatine, destroyed this nutritive quality. The very bones which, when raw,
supported life, failed utterly when boiled.
We call especial attention to the fact of the very small proportions of Albumen which exist in the bones, as strikingly confirming our hypothesis respecting the power of the organism to form Albumen for itself, if a small amount be present to act as a sort of leaven. Moleschott also maintains, on other grounds, that Gelatine must be converted into Albumen, since the amount of Albumen in bones is in itself utterly insufficient for the demands of the tissues;* and Mulder points to the fact that, when an animal is fed on Gelatine, we never find this substance passing away in the excreta: a sufficient proof that it must in some way have been incorporated with the organism, or decomposed in it, to subserve the purposes of nutrition.t
Liebig, obliged by evidence to admit some nutritive quality in Gelatine, suggests that it is confined to the formation of the gelatinous tissues. This is one of those hypotheses which seduce by their plausibility, and accordingly it has been generally adopted, although physiological scrutiny detects that this is precisely one of the uses to which Gelatine can not be turned. For on the one hand we see that the herbivora have gelatinous tissues, although they eat no Gelatine; and, on the other hand, we see that even the carnivora, who do obtain it in their ordinary food, cannot form their gelatinous tissues out of it, because it is never in their blood, from which all the tissues are formed.
Bernard has shown that part of the Gelatine is converted into sugar, and sugar, we know, is necessary to the organism. It may also be converted into fat; and, as has been said, there is much evidence to show that it may be converted into Albumen among the complex processes of vital chemistry; but whatever may be the decision respecting the point, there can be no legitimate reason for denying that Gelatine ranks among nutritive principles.
Fats and Oils.-These are various
* MOLESCHOTT, Kreislauf des Lebens, p. 135.
+ MULDER, p. 937.
Fats and oils are all difficult of digestion-more so, indeed, than most other principles; but the degree in which they are digestible is very much a matter of individual peculiarity, some men digesting large quantities with ease, others being unable to digest even small quantities. M. Berthé instituted an elaborate series of experiments on his own person, with the view of ascertaining the comparative digestibility of various fats and oils. The following classification of his results is all we can find space for. First class, comprising those difficult of digestion : Olive oil, almond oil, poppy-seed oil. Second class, comprising those easy of digestion: Whale oil, butter and animal fats, colourless liver-oil. Third class, comprising those very easy of digestion: Pure liver-oil.
It should be remembered that great differences are observable according to the state in which oils are ingested. If taken by themselves, they are scarcely affected by the digestive process, and act as laxatives; but if taken mingled with other substances, they may be reduced to an emulsion,
* PEREIRA: Treatise on Diet, p. 167.
and so absorbed. Thus we eat olive oil with salad, or butter with bread, and the greater part is absorbed; but the same amount of olive oil administered alone would act as a purge. It is owing, moreover, to the minute state of subdivision and mixture of the oils in all vegetable substances that they are so much more digestible than animal fats.
Dr Pereira quotes the statement of Dr Beaumont, that "bile is seldom found in the stomach, except under peculiar circumstances. I have observed that when the use of fat or oily food has been persevered in for some time, there is generally a presence of bile in the gastric fluids." Upon which Dr Pereira remarks that the popular notion of oily or fatty foods "causing bile" is not so groundless as medical men have generally supposed. The reason of fat being indigestible is thus suggested :
does not become properly chymified. It "In many dyspeptic individuals, fat
floats on the contents of the stomach in
the form of an oily pellicle, becoming odorous, and sometimes highly rancid, and in this state excites heartburn, nausea, and eructations, or at times actual vomiting. It appears to me that the greater tendency which some oily substances have than others to disturb the stomach, depends on the greater facility with which they evolve volatile fatty acids, which are for the most part exceedingly acrid and irritating. The unpleasant and distressing feelings excited in many dyspeptics by the ingestion of mutton-fat, butter, and fish-oils are in this way readily accounted for, since all these substances contain each one or more volatile acids to which they owe their odour. Thus mutton-fat contains hircic acid; butter, no less than
three volatile acids, viz. butyric, capric, and caproic acids; while train-oil contains phocenic acid." ‡
The effect of a high temperature on fat is to render it still more unsuitable to the stomach; and all persons troubled with an awful consciousness of what digestion is, and not living in that happy eupeptic ignorance which only knows digestion by name, should
+ BERTHE: Moniteur des Hôpitaux, 1856, No. 69. CANNSTATT: Jahresbericht 1856, pp. 69-72.
PEREIRA, p. 171.