The earliest authorities on the thyroid gland, including Schiff and others, have shown that when this gland is extirpated in a dog, as a rule the animal develops convulsions after a few days, and subsequently dies. It is very unusual to find a longer survival after such operations.

Interesting and very instructive experiments by the American specialist, Dr. Leo Breisacher, of Detroit, Mich. (formerly assistant to Professor Munk, of Berlin), have demonstrated that it is possible to keep animals, operated on as above, alive for a long time if they are debarred from meat and kept on a milk diet.

A perfectly natural explanation of this prolonged survival, which had never been observed until the above experiments, lies in the fact that milk food is better adapted to animals deprived of their thyroid, and that, as Dr. Breisacher maintained, meat acts in a poisonous manner on the nervous system of dogs thus operated on. Thus we note that dogs in this condition cannot live on a meat diet. The learned savant and others noticed that dogs so fed succumbed very quickly, while at the same time he observed that no attack of convulsions ever occurred in dogs fed on milk, though many other authorities had noticed such symptoms in corresponding cases.

He also observed,—and it is a most interesting point,—that dogs which improved on a milk diet, again got worse after meat or bouillon was taken and died in consequence. Of great importance also is his observation that boiled meat is not dangerous to animals thus operated upon, which he explains as being due to the fact that the extracts of meat having a toxic action are soluble in water.

There can thus be no doubt, from these beautiful experiments of Breisacher, that meat does contain substances that are poisonous, and we may safely draw the conclusion therefrom that if we, who are in possession of our thyroid, do not suffer from a meat diet, it is due to the protection afforded us by this gland. If we remove this, as in the instances given of the dogs, or if it is degenerated by disease, then our immunity also disappears. In myxœdematous people this is self-evident, for they are always worse after taking meat, and most of them have an antipathy to this sort of food. Also in many cases of severe diabetes (a myxœdematous condition), meat is very injurious, and if taken in large quantities can contribute to the development of acidosis.^[170]

The above-mentioned experiments of Breisacher have been confirmed by F. Blum, of Frankfort. He finds also that omnivorous animals operated on as the dogs, if fed with meat, die from tetany in a few days. But when such animals have been kept on milk for a long time, before and after the operation, a large proportion have survived, or, at most, passed through a mild form of tetany, and continued well until meat was again administered, when their condition soon became worse, and death ensued, as in the case of the animals kept on a meat diet. Some of the dogs fed on milk also died, but before succumbing they underwent a long cachectic illness. In any event they lived longer than the animals fed with meat, which rapidly died with violent symptoms.

Dr. Blum arrived at the conclusion that the thyroid is a disintoxicating organ (entgiftendes organ) the function of which is to destroy poisonous products formed by the decomposition of the albuminous food-substances.^[171]

The Japanese authority, Kishi, also arrived at the same conclusion, after having removed the thyroid gland from 150 monkeys, dogs, and other animals.

That the products of the decomposition of albuminoids can produce changes in the thyroid has been proved by Galeotti and Lindemann, who found an increase of colloid substance in the thyroid of animals after the injection of leucin and tyrosin,—which are the products of decomposition of albuminous substances. That meat acts in an injurious manner on the thyroid gland, if eaten in very large quantities, has been proved by clinical observations and by the experiments of Chalmers Watson, into which we shall enter more fully in the chapter on the dangers of too free a meat diet.

The thyroid not only protects us against the poisons in meat, but also against many others; in fact, perhaps we may say, against poisons generally. Let us, however, specially mention those poisonous products which have been tried experimentally. That the thyroid protects the body against bacillary attacks has been noted by Charrin in the case of dogs, which succumb in a very short time to all kinds of infection after the removal of the thyroid. We have demonstrated, in Chapter III, the protective action of the gland against such poisons as chloroform, as mentioned in our communication to the Paris Biological Society in 1906, where we stated that in chloroform narcosis all the characteristics of an increased activity of the thyroid are perceived,—including symptoms such as we see in Graves’s disease. We have also found that the thyroid of dogs contains an increased amount of colloid substance after chloroform narcosis, which enables us to understand why this drug is not well borne by animals operated upon as above, as discovered by Lanz and by Walter Edmunds; likewise, we may thereby explain why patients suffering from Graves’s disease of long standing, in which there generally is a transition to a myxœdematous condition, are liable to a fatal termination after an operation with anesthesia. Cases of diabetes (in accord with frequency of thyroid changes) also often present serious phenomena after an operation under anesthesia, including coma and even death.

Alcohol also acts on the thyroid gland, there being a certain analogy between intoxication by chloroform and by alcohol. The changes in the thyroid after the long-continued use of alcohol are the consequences of the frequent conditions of hyperactivity of this gland, expressive of its antitoxic action. We have referred to the influence of alcohol on the thyroid in other parts of this book. This gland also protects us against injurious drugs. Hunt, of Washington, has shown from experiments that when certain animals, such as rabbits, have been given acetonitril and thyroid preparations at the same time, they do not become poisoned; whereas when they have taken the former alone, they do. Jeandelize and Perrin have also proved the protective action of the thyroid against arsenic.

Garnier has also found that certain drugs, such as iodine, pilocarpin, etc., when injected into animals, produce an increase of colloid secretion in the thyroid glands. It is, therefore, but logical to regard this hyperactivity of the thyroid gland as an expression of its defensive action against toxic products (see Chapter III).

From the foregoing it is obvious what an important organ we possess in the thyroid gland, and that by its degeneration, as in the state of myxœdema or in the much more frequent athyroidia, we become more exposed to all kinds of poisonous products; but what renders its degeneration a still graver misfortune for us, is the fact that it is apt to bring about the degeneration also of other organs which destroy and eliminate poisonous products, viz.: the liver, kidneys, intestines, and skin.

The liver is always altered by extirpation of the thyroid gland, likewise as a rule in myxœdema, and even in hypothyroidia; for congestion and other changes follow, as found by Rogowitch, Sanquirico, and Canales, Albertoni, Tizzoni, and others. A fatty degeneration of the liver has also been described by Sciolla.

Laulanié has discovered, in the same way as Van der Ecke and Rosenblath, very extensive changes in the liver after removal of the thyroid. Jeandelize also found interstitial hepatitis after the removal of the thyroid and parathyroids. Kishi also describes alterations in the blood-vessels of the liver occurring in a great number of animals after thyroidectomy.

Hun, Prudden, Mackenzie, G. Murray, and others, found usually a cirrhosis of the liver in myxœdematous persons. Vermehren found an interstitial hepatitis, with thickening of the blood-vessels of the liver, and of the bile, in myxœdema.

It is also of great significance to note that Gley, Laulanié, and others, constantly found biliary matters present in the urine of animals from which the thyroid had been removed.

After due consideration of these facts it cannot be denied that the liver and the thyroid stand in very close relationship, and this we maintained at the last French Congress of Medicine at Liège, where we were glad to see that the President of the Congress, Professor Bouchard of Paris, and later Professor Neusser of Vienna, coincided in this opinion.

We have also shown, as already mentioned (Chapter V), that degenerative processes of the thyroid are able to facilitate the development of the gall-stone complaint. The degeneration of the thyroid is not only followed by degeneration of the liver, but also by that of the kidneys.

It has been noted by Albertoni and Tizzoni, that animals whose thyroid has been removed show a condition of interstitial nephritis. Blum has found the same thing, and has observed also that this condition frequently comes about in an astonishingly short time after the operation, say, in 18 to 20 days. The parenchyma also presents distinct signs of inflammation; the urinary channels lose their epithelium and present the appearance of hollow grooves. These changes occur in all animals, except such as die a few days after the operation, and such as are permanently immune from the intoxication that follows the removal of the thyroid.

We can also observe clinically that removal or degeneration of the thyroid are capable of producing changes in the kidneys; for after the operation, as a rule, albumin appears in the urine.

In myxœdema and hypothyroidia there is also very frequently albumin in the urine, as well as hyalin or granular casts. In such cases the urine is usually not copious; very frequently it is scanty (oliguria), and its light color and low specific gravity show that the solids have been retained in the body. In such cases there is often retention of uric acid. In a communication to the Paris Biological Society (February 25, 1905) we attributed gout to changes in the kidneys giving retention of uric acid, after primary alterations of the thyroid as the cause (see also Chapter V).

That the intestines also suffer changes after degeneration of the thyroid is best established by the fact that there is obstinate constipation in such cases,—as in myxœdema or in partial myxœdema and hypothyroidia (old age). The functions of the skin also will be diminished after degeneration of the thyroid, as we observe plainly in the conditions of myxœdema and hypothyroidia. In these diseased conditions there is an atrophy of the sudorific and sebaceous glands, so that the skin cannot perspire; on this account a large amount of toxic products is retained.

We can see plainly from the above that when a person has a degenerated thyroid a condition of auto-intoxication must necessarily follow, as there is in consequence a degeneration also of the other organs which destroy and eliminate poisonous materials. The liver in such a case will not be able to fulfill its function of destroying a mass of poisonous substances; the sluggish kidneys and bowels will not eliminate them sufficiently, and dry skin will also contribute to their retention, since its insensible respiration is not taking place. All these life-shortening agencies, which may combine to cause premature old age, can be brought back to a primary cause—the degeneration of the thyroid gland.

When the thyroid is removed from an animal, but the parathyroids are allowed to remain, that animal will not then suffer convulsions, but will only present the symptoms of cachexia typical of the operative cases of myxœdema.

It has been shown by Gley, Vassale, and Generali, that these very small glandular organs, of which there are four, two internal and two external ones, possess quite a different structure from the thyroid gland.

It has been demonstrated by many authorities, among them Jeandelize, that the convulsions which follow the removal of the thyroid are due to the fact that the parathyroids have been removed completely, together with the thyroid gland. Jeandelize was able to produce convulsions by merely removing the parathyroids alone; he attributed tetany and epilepsy to the changes in the parathyroids, in common with other authorities, who have even obtained good results in epilepsy with parathyroid treatment.

Several authorities besides Jeandelize have attributed tetany to alterations of the parathyroids: for instance, Pineles; and at the German Congress of Medicine in Munich, Erdheim communicated his observations in three cases of tetany, in each of which, at the post-mortem, there was found hypertrophy of the parathyroids.

Dr. Macallum, of Johns Hopkins University, has also reported the case of a person who developed tetany in consequence of a dilatation of the stomach, and in whom the parathyroids were found to be hypertrophied.

We learn from the foregoing that the parathyroids protect us against poisons that arise from the stagnation of the contents of the stomach, and that their integrity is necessary as a safeguard against important alterations of the nervous system.

However, these glands, which were already described by Sandström twenty-two years ago, have not been studied as yet to the same extent as the thyroid, and we cannot enlarge further on this subject at the present time.