After the food has been prepared and taken up by the blood, as described in the preceding chapter, it is carried to the liver by the portal vein. Here the most injurious and poisonous substances are destroyed by the liver, or are trans-formed into innocuous compounds. Poisons which have not been broken up by the action of the hydrochloric acid can be destroyed by the liver, and it is for this reason that poisonous substances which would cause certain death if absorbed through the skin lose their effect when taken into the stomach. Thus, for instance, the venom of many snakes which causes instant death through a slight wound of the skin is, when swallowed by the mouth, quite harmless. The liver is one of our most powerful detoxicating organs, and, in order to enable it to carry out this function successfully, the quality of the food taken is of importance; when the nourishment is insufficient, or when there is not a sufficient quantity of albumin, the liver, as the experiments of Roger and Garnier have shown, is unable to do its work. The poisons combine with the albuminoid bodies of the liver, and, consequently, animals which have been given large quantities of albumin are much better protected against poisoning by metals, such as quicksilver, by arsenic, and by various alkaloids than other animals not so treated. When the liver has been kept long at work in antagonizing poisons such as alcohol, tobacco, etc., its integrity suffers. Inflammatory processes may occur in this very important organ, causing the loss of its protective tissues. The poisonous end-products of the metabolism of albumins are themselves rendered non-toxic by the liver, and the ammoniacal compounds are excreted in the harmless form of urea. This ammonia-detoxicating function of the liver is of the greatest importance for us. In severe diseases of the liver it is naturally much impaired, and it then becomes advisable to refrain, in so far as possible, from a diet containing albumin.
In addition to the formation of urea, the liver also plays a major rôle in the metabolism of the carbohydrates. As we have seen, the carbohydrates, such as starch, are first trans-formed into grape-sugar. This is then carried into the liver by the portal vein, and the sugar is there stored up as glycogen. Thus, the liver forms a sort of preliminary storehouse for the sugar’ needed by the organism. The glycogen is given out as it is required, is transformed into sugar by a ferment contained in the liver, and is, as such, excreted and carried into the tissues. Here it is again stored up in the muscles, so that both the liver and the muscles accumulate the sugar in the form of glycogen. When the muscles are required to perform any sort of work, they give up the glycogen for this purpose. Muscular work is thus carried out through the agency of the carbohydrates. After prolonged and fatiguing labor, the liver contains only a small amount of glycogen, as it gives off its reserve of that substance much more freely than the muscles. In hunger the same thing occurs. It should be mentioned that the liver forms the glycogen not only from the carbohydrates, but also from the albumins; some forms of albumin, e.g., egg-albumin, em-body molecules of carbohydrate. The liver is also a laboratory or preparatory room for the fat which is carried to it with the food by the portal vein. When sugar is not burned up and is not voided with the urine, so that it is still available for subsequent use, it is converted into fat, and this process is likewise carried out by the liver.
Another substance of great importance in digestion is formed in the liver, viz., the bile, the functions of which we have already described.
From the liver the substances which are to serve as food for the body pass with the blood through the lower vena cava to the heart. This important organ is also influenced by the quality and quantity of the food. When, for instance, large quantities of fluids are taken, it is placed under greater stress. When such excessive amounts of fluid are carried to the heart during a long period, they may cause structural changes, such as induration of the musculature, and later on a dilatation of its cavity, such as we see in the so-called “Munich beer heart.” A diet too rich in albumins and containing a considerable amount of extractives, as well as a continued rich diet in general, may also affect the integrity of the heart. For the action of the heart muscles as well as for the muscles in general, a carbohydrate diet is the best. Alcohol and coffee or tea in large quantities and after long-continued use may also exert a very injurious influence upon the heart.
Such errors in diet are very harmful to the blood-vessels. The pressure in them is augmented, and when a high blood-pressure is maintained for a long time the production of arteriosclerosis is greatly favored. The decomposition products resulting from a diet rich in albumins, along with the extract-ives simultaneously contained in the blood, cause very serious results after their action on the vessels has persisted for some time. According to Huchard, Senator, and others, arteriosclerosis is very readily produced in this way, and many cases are certainly due to an injudicious one-sided diet.
Overindulgence in coffee and tea may cause a change in the tonus of the blood-vessels, and the constant dilatation will cause untoward effects, as described by Romberg. Tobacco, in particular, has a most injurious action upon the walls of the blood-vessels, and a great many cases of arteriosclerosis are due to its use. Alcohol, too, when continuously and considerably indulged in, is harmful to the blood-vessels. Large quantities of fluid, by overloading the vascular system, are most hurtful to the organism.
Food exerts a marked influence upon the constitution of the blood itself. Excessive amounts of fluid may cause a dilution of the blood owing to the absorption of the water; this, however, is of short duration, as the fluid which has been taken up is soon excreted. On the other hand, it is conceivable that, when such quantities of fluid are habitually absorbed, more permanent dilution of the blood, and a watery condition of the tissues, may result.
With too dry a diet, the blood may become inspissated. When a large quantity of hot tea is taken, causing excessive perspiration, the same result may be produced; but such a thickening of the blood will be of short duration. The fluid contained in the tissues is then drawn out, a condition which is also observed after severe hemorrhages.
Dilution of the blood may also occur, as has been shown by the very exact experiments of Grawitz, when the diet is insufficient and too poor in albumin.
In regard to the effect of diet upon the condition and the composition of the blood, we here see manifested, as almost universally in the nutrition of man and of animals, the principle that the amount of the individual constituents of the blood depends in large measure upon the quantity of such substances ingested in the food. The blood contains more albumin than it does carbohydrates and fat. Many nutritive salts, however, are also to be found in it; the blood of pigs, indeed, is especially rich in iron.
The albumin-content of the blood plays a very important rôle, and when too little of this substance is carried into the blood from the food very injurious effects may result. As we have seen, the blood-serum becomes too watery, and the red corpuscles are also impaired. When animals are fed upon meat, the hemoglobin content is increased ;1 on the other hand, Bischoff and Voit found that by placing carnivorous animals upon a bread diet the blood was rendered more watery.
Leichtenstern, by researches carried out on his own blood, showed that a considerable increase of the hemoglobin content of the blood took place upon a plentiful diet.
While an insufficient supply of albumin is prejudicial to the composition of the blood, an overgenerous supply, on the other hand, may result in the formation of considerable quantities of injurious constituents, such as uric acid. This is in-variably produced in large amounts with a generous meat diet, especially one rich in cell nuclei, i.e., consisting of the glandular organs, liver, sweetbreads, as well as brains, etc. Not only meat, but many vegetables as well, and especially the leguminous varieties, may have an injurious effect, owing to the “purin bases” contained in them, from which the uric acid is formed. Tea and coffee have the same effect. We shall later refer to this in greater detail, and present a table of the content of uric-acid-producing substances in the various articles of food.
The blood also contains a certain quantity of sugar, not usually exceeding OE’ per cent. When, however, an excessive amount of sugar is taken at one time it may happen that the sugar will not all be taken up by the liver, and the excess will then, since it cannot be so rapidly consumed, be excreted as a foreign body by the kidneys.
In many persons this may occur even after the ingestion of articles of food rich in starch, and when this takes place very often we have to deal with diabetes mellitus. The combustion of sugar, as well as its storing up in the liver, is regulated by the pancreas through the agency of a ferment which is probably secreted by an epithelial structure of the islets of Langerhans present in the pancreatic tissue. When the pancreas is re-moved, diabetes is certain to occur.
The food also exerts a great influence upon the circulation of the blood in the vascular system.
The friction of the blood during its passage through the lumen of the blood-vessels is said to be greatly increased by a diet rich in albumins (i.e., meat), as shown by the experiments of Determann. Alcohol, tea, etc., have the same effect.
Whether, on the other hand, a diet rich in uric acid will impart to the blood a viscid consistency,collemia,as claimed by Haig, has not yet been proven experimentally.
The various constituents of the food are carried to the organs of the body by the blood, and the products of their transformation, such as urea, together with various poisonous and injurious substances which have not been destroyed by the liver, finally reach the kidneys, and are here eliminated from the blood. Alcohol, strong spices, etc., thus exert their harmful influence upon the lining epithelia of the urinary canals, a certain portion of these cells being naturally lost, as is shown by the presence of hyaline casts in the urine. Indeed, we should always remember that everything we eat must pass through the kidneys, and may there prove injurious. Even in the process of excretion of the wastes from our ordinary diet, particularly an albuminous diet when it contains many ex-tractive substances, the kidneys, after the steady work of many years, may suffer injury. A meat diet, owing to the nature of the end-products formed, imposes heavier work upon the kidneys than does a diet of vegetables or one consisting principally of milk ;much more urea and uric acid is secreted in the former case. When the work of the kidneys is not fully performed, the excretion of uric acid is accomplished with difficulty, and gout develops easily.
An overgenerous meat diet may also give rise to diabetes, probably through its influence upon the thyroid gland (Lorand). The thyroid greatly influences the metabolism of sugar, since, as I have shown, sugar is oftenest excreted when the thyroid gland is overactive. On the other hand, very large quantities of sugar may be taken without any alimentary excretion of sugar when the thyroid gland is degenerated.
The excretion of sugar resulting from overactivity of the thyroid is not only induced by large quantities of sugar or very starchy foods, but also in the absence of carbohydrates when a meat diet is taken. When there is an abundance of thyroid secretion it causes disintegration of the albumin, and much more sugar may be formed than the amount corresponding to the carbohydrate molecules of the albumin; we must there-fore admit the presence of a toxic irritation of the tissues. When the pancreas is active this sugar excretion may only be temporary, but when it is incapacitated by disease permanent diabetes is developed. As I have proven experimentally, there exists a kind of antagonism between the thyroid and the pancreatic gland, so that when the pancreas is removed the thyroid becomes overactive; when, however, the thyroid gland is extirpated, the pancreas shows an increase of the islets of Langerhans, which, as has already been mentioned, probably regulate the consumption of sugar in our bodies. As I have previously demonstrated, diabetes is caused by one of two factors : I. Degeneration of the pancreas. 2. Overactivity of the thyroid gland.
The excessive activity of the thyroid gland may be caused by a faulty diet, which can in this way cause diabetes, especially when there is an inherited tendency. A meat diet containing many extractive substances exerts, as has been shown by the experiments of Breisacher, Blum, and Chalmers Watson, which will be further referred to, later, an irritating influence upon the thyroid, and in persons who continue for years to eat too much meat, and besides indulge to excess in sweets, diabetes is easily developed.
The thyroid also greatly influences the metabolism of fats, and we may say, in general, that it, in connection with the other ductless glands, in fact regulates the metabolic processes of the organism; it acts, as von Noorden says, as a kind of bellows for the processes of combustion. When the thyroid is degenerated and inactive, obesity develops readily, especially when fat-forming substances, such as fats or carbohydrates, are taken, together with a sufficient quantity of albumins. When, on the contrary, the thyroid gland is overactive, emaciation occurs, and the same condition may be brought about by the administration of thyroid extract.
Alcohol, like a meat diet, also has a stimulating action upon the thyroid. Excessive use of alcohol can, in the same way as long-continued indulgence in a diet rich in meats, pro-duce a change from the previous condition of overactivity to one of underactivity and degeneration of this very important gland, which exerts an influence upon all the life processes of our organisms. (See various chapters in my book on “Old Age Deferred.”)
The marked importance of the rôle played by the thyroid in the human nutritive functions is due to the fact that in addition to its influence upon metabolism it also acts upon the poisons which are taken into the body with the food. According to Blum, it detoxicates products which are formed through the disintegration of albumin ; the experiments of Kishi also support this view. For its action upon other poisons absorbed in part with the food and drink (as alcohol) I would refer the reader to my work mentioned above.
The other ductless glands, including the hypophysis, the adrenals, the sexual glands, exert similar detoxicating actions, and they, likewise, are variously influenced by different foods. Alcohol, for instance, acts upon the adrenals and the sexual glands. After feeding upon meat, a change in the hypophysis has been observed in birds of prey (Forsyth). The influence of food upon the sexual glands and sexual activity will be taken up later.