Page images
PDF
EPUB

the phagocytosis of nerve-cells, I shall not attempt a discussion of the problem.

Although the destruction of nerve-cells by neuronophags is a general occurrence in senile brains, one may conceive of cases where this does not occur. And so, in old people who have preserved their faculties, it may well be that the neuronophags have refrained from attacking the nerve-cells.

[graphic][graphic][merged small][merged small]

FIGS. 6. & 7.-Two nerve-cells from the cortex of the brain of an old dog aged

fifteen years.

The neuronophags surrounding the nerve-cells contain numerous granulations. (From preparations made by M. Manouélian.)

But as such instances are rare, so also phagocytosis is usually found in senile brains, and I cannot accept M. Sand's denial of its existence, based on his study of two

cases.

The general result of my investigation into the criticisms. that have been published on this matter has confirmed me in my belief that neuronophagy plays a most important

part in senescence, and recent observations that I have made with M. Weinberg have completely supported this view.

The bleaching of hair and the atrophy of the brain in old age thus furnish important arguments against the view that senescence is the result of arrest of the reproductive powers of cells. Hairs grow old and become white without ceasing to grow. The cessation of the power of reproduction cannot be the cause of the senescence of braincells, for these cells do not reproduce even in youth.

III

MECHANISM OF SENILITY

Action of the macrophags in destroying the higher cellsSenile degeneration of muscular fibres-Atrophy of the skeleton-Atheroma and arterial sclerosis-Theory that old age is due to alteration in the vascular glands-Organic tissues that resist phagocytosis

THE instances which I have selected in attempting to describe the mechanism of senescence of the tissues are not the only cases in which the importance of phagocytosis is evident. The blanching of hair is due to the destructive agency of chromophags; in atrophy of the brain neuronophags destroy the higher nerve-cells. In addition to these instances of phagocytosis, in which the active agents belong to the category of macrophags, there are many other devouring cells, adrift in the tissues of the aged, and ready to cause destruction of other cells of the higher type. The phagocytic action is not so manifest as in the case of infectious diseases, partly because it is the method of macrophags to absorb the contents of the higher cells extremely slowly. The mode of action is well seen in the atrophy of an egg-cell (Fig. 8), where the surrounding macrophags gradually seize hold of the granules within it and carry these off. As the process goes on, the ovum becomes reduced to a shapeless mass, and finally leaves only a few

1

fragments, or disappears completely. M. Matchinsky 1 has studied the series of events in my laboratory, and I am myself well assured of the importance of the action of macrophags in the atrophy of the ovary.

The phenomena of atrophy in general and of senile decay afford other cases of tissue destruction in which the phago

[graphic]

FIG. 8.-Ovum of a Bitch in process of destruction by Phagocytes, which are full of fatty granules. (After M. Matchinsky.)

cytic character of the process is more modified and obscure than in nerve-cells and ova.

It is well known that progressive muscular debility is an accompaniment of old age. Physical work is seldom given to men over sixty years of age, as it is notorious that they are less capable of it. Their muscular movements are feebler and soon bring on fatigue; their actions are slow and painful. Even old men whose mental vigour is unimpaired admit their muscular weakness. The physical

1 Annales de l'Institut Pasteur, 1900, vol. xiv. p. 113.

correlate of this condition is an actual atrophy of the muscles, and has for long been known to observers. More than half a century ago, Kölliker, one of the founders of histology, devoted some attention to this matter, and described the senile modification of muscular tissue in the following words :-" In old age there is a true atrophy of the muscles. The fibres are much more slender; there are deposited in their substance numerous yellow or brown granules and many globular nuclei. These nuclei are frequently arranged in longitudinal series and present such signs of active division as are found in embryonic tissue." Other investigators afterwards made similar observations. Vulpian 2 and Douaud 3 have stated that a multiplication of nuclei takes places in the atrophying muscles of the old.

As the senile degeneration of muscular tissue appeared to be important in my study of the mechanism of senescence, M. Weinberg and I examined several cases of muscular atrophy in old human beings and lower animals. We were able to recognise the phenomena observed by our predecessors. In senile atrophy the muscular fibres contain many nuclei, and these, increasing rapidly, bring about an almost complete disappearance of the contractile substance (Fig. 9). The fibres preserve their striation for a certain time but eventually lose it and appear to contain an amorphous mass with numerous, rapidly multiplying nuclei.

The investigators who had recorded these facts thought of them only as curious. It is plain, in the first place, however, that this remarkable and rapid multiplication is a proof that senile atrophy is not due to failure of cell pro

1 Eléments d'histologie humaine, French translation, 1856, p. 222. 2 Leçons sur la physiologie du système nerveux, 1866.

3 De la dégénérescence graisseuse des muscles chez des vieillards. Paris, 1867.

« PreviousContinue »