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in old people the thyroid and the suprarenals frequently show cystic degeneration. It is quite probable, therefore, that these so-called vascular glands have their share in producing senility. Many facts show that they destroy certain poisons which have entered the body, and it is easy to see that, if they have become functionless, the tissues are threatened with poisoning. It does not follow, however, that their action in producing senility is exclusive, or even preponderating. M. Weinberg, at the Pasteur Institute, made special investigations on this point, and found that the thyroid gland and the suprarenal capsules were almost invariably normal in old animals (cat, dog, horse), although the latter showed unmistakable signs of senility. Similarly in an old man of 80 years, who died from pneumonia, the thyroid gland was quite normal.

It must not be forgotten that the aged very often die from infectious diseases such as pneumonia, tuberculosis, and erysipelas. In these diseases the vascular glands. generally, and the thyroid gland in particular, are very often affected, with the result that what is due to infection has been set down as a symptom of old age.1

Although the appearance of patients from whom the thyroid gland has been removed, or in whom it has degenerated spontaneously, recalls that of old people, it is possible to exaggerate the similarity. In the masterly accounts of such unfortunates, recently compiled by the well-known surgeon Kocher there are many points which are characteristic, without being typical, of old people.

Oedema of the skin which characterises thyroid patients

1 Sarbach, Mittheilungen a. d. Grenzgeb. d. Med. u. Chir., vol. xv. 1906.

2 Verhandlungen d. Kongr. f. innere Medicin. Wiesbaden, 1906, pp. 59, 98.

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is by no means usual in old age. The loss of hair, normal in the patients, is not a character of old age. In myxedematous women, menstruation is very active; it ceases in old women. The great muscular development of myxedematous patients distinguishes them from old people.

1

Physiological investigation does not support the existence of any strong affinity between old age and affection of the thyroid gland. It is known that removal of the thyroid is followed by cachexia only in young subjects, MM. Bourneville and Bricon having shown that the tendency to cachexia after extirpation of the thyroid ceases almost abruptly at the age of thirty. That age may be taken as the limit of youth, of the time when growth is vigorous and the function of the thyroid most active. Cases of cachexia, where the thyroid gland has been removed in old persons from fifty to seventy, are very.rare.

2

Rodents (rats, rabbits) support the removal of the thyroid extremely well, without signs of cachexia, although these are normally short-lived creatures. According to Horsley extirpation of the thyroid is not followed by cachexia in birds or rodents and is followed by it only very slowly in ruminants and horses; it produces the condition invariably but slightly in man and monkeys and extremely seriously in carnivora. If this series be compared with the information given in the next section of this volume on the relative ages which the animals in question attain, it will be seen that there is no correspondence.

In short, whilst I do not deny that the vascular glands may take a share in the causation of senility, in so far as

1 Archives de Neurologie, 1886.

"Die Function d. Schilddrüse, Virchow's Festschrift, vol. i. 1891, p. 369.

they are destroyers of poisons, I cannot agree with the theory of Dr. Lorand.

I think it indubitable that in senescence the most active factor is some alteration in the higher cells of the body, accompanied by a destruction of these by macrophags which gradually usurp the places of the higher elements and replace them by fibrous tissue. Such a process affects the organs of secretion (kidneys), the reproductive organs, and in a modified form the skin, the mucous membranes, and the skeleton. The testes are amongst the organs which resist invasion by macrophags. I have already given an example ("The Nature of Man," p. 98) of an old man of 94 in whom active spermatozoa were produced. I know of a similar case, the age being 103 years. Such cases are not rare, and not only in old men, but in old animals, the testes continue to be active. Dr. Weinberg and I have investigated these organs in a dog which died at the age of 22 years after several years of pronounced senility. Many of the organs of the animal exhibited serious invasions by macrophags but the testes were extremely active, the cells being in free proliferation and producing abundant spermatozoa (Fig. 11). In harmony with this condition of the sexual organs, the sexual instincts of the animal remained normal. We have investigated another dog which died at the age of eighteen years. In this case the testes were cancerous and there was no possibility of the production of spermatozoa. None the less, this dog although markedly

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FIG. 11.-Testis tissue from a dog aged twenty-two years. (From a preparation made by Dr. Weinberg.)

senile (Fig. 12) still showed sexual instincts until shortly before it died.

It is manifest that the tissues do not invariably degenerate in old age, nor do all the organs that are modified in old age show destruction by phagocytes and replacement by connective tissue. Organs which produce phagocytes, such as the spleen, the spinal marrow and the lymphatic glands, certainly show traces in old age of fibrous degenera

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tion but remain sufficiently active to produce macrophags which destroy the higher cellular elements of the body. I have frequently noticed cell division in such organs, and as an example may give the case of the bone marrow taken from a man of 81 years (Fig. 13).

The eye is an organ that is modified in old age without the action of macrophags. Cataract and the senile arc which appears as a milky ring at the edge of the cornea

are frequent in old age. These modifications are due to impregnation of the parts affected by fatty matter which makes them opaque. This deposition of fat1 has been attributed to defective nutrition. In most organs such fatty degeneration is followed by phagocytosis, but the cornea and the crystalline lens are exempt from this consequence for anatomical reasons. Most organs possess in addition to their higher elements a constant source of macrophags. Such a source of phagocytosis is the neurogloea in nervous tissues, the sarcoplasm in muscular tissues; the bones contain osteoclasts and the liver and the kidneys are readily invaded by phagocytes from the blood. The lens and the cornea have no cells that are able to become macrophags.

FIG. 13.-Bone marrow from the sternum of a man aged eighty

one years.

(From a preparation made by Dr. Weinberg.)

Some infectious diseases bring about precocious senility. A syphilitic child is "a miniature old man, with wrinkled face, skin dull and discoloured and flabby and hanging in folds as if it were too large." In such a case the active agent is the microbe of syphilis which has poisoned the child on the breast of its mother. It is no mere analogy to suppose that human senescence is the result of a slow but chronic poisoning of the organism. Such poisons, if not completely destroyed or eliminated, weaken the tissues, the functions of which become altered or enfeebled, so that, 1 Fuss, Der Greisenbogen, in Virchow's Archiv, 1905, vol. clxxxii. p. 407; S. Toufesco, Sur le cristallin, Paris, 1906.

2 Edmond Fournier, Stigmates dystrophiques de l'hérédosyphilis, Paris, 1898, p. 4.

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