Senescence, the Last Half of Life

by G. Stanley Hall

Sir James Crichton-Browne’s long article[145] is a classic and is based on very comprehensive statistical and other studies. He tells physicians that it should be their great aim to grow old themselves and to be the cause of old age in others. The marked increase in the duration of life in recent decades has been almost entirely confined to its early stages. After 45 the decline in the death rate has been insignificant; and after 65, as we have elsewhere seen, it has actually increased. Thus the proportion of men ripened by experience has in fact declined. What carries off the old? Not fever, smallpox, or phthisis chiefly, as was once the case, but the following in order of frequency: cancer, heart diseases, nervous troubles, and kidney complaints, and these are all degenerative diseases due not so much to intemperance as to the new strains of modern life, which are less felt in the country and less by women.

Society needs to have life lengthened instead of abbreviated at its extreme end but men and women to-day are growing old before their time. We often have deaths reported to be from old age between 45 and 55. Indeed, atrophy and debility often come prematurely. The long-sightedness of old age seems to begin earlier than it used to do and the increased number of those who wear glasses cannot be entirely explained by better diagnosis. It is quite clear that those who live in hot climates show these optical symptoms of old age earlier than Europeans. The teeth, too, are certainly degenerating earlier than formerly, and early baldness is probably increasing still more. Senile insanity or atrophy of the brain is certainly more common and appears earlier. It abounds in our metropolitan asylums where human wreckage accumulates. Very many enter the outer circles of melancholia without proceeding to dementia and still fewer proceed to suicide, the rate of which is also rapidly increasing after 45. Touches of this kind of depression are very often felt at the turning point of life or soon after, perhaps at the first discovery of gray hairs, and many are tormented in private and perhaps in the silent watches of the night by the realization that youth is leaving them. Such, however, is the law of nature, for even the stars and planets grow old, as we know by their spectra. The voice is not normally shrill or quavering but may be very strong unless the crop of wild oats, which always ripens in later years, is too rank. Conscience may awaken near the turn, especially if too many dregs have accumulated in the cup of life or the machinery has been overstrained. The fact is, the infirmities often attached to age may, each of them, in single cases be absent, so that typical old age is rare, and any one of them is far less prevalent than is generally supposed.

Our life is made up of a series of evolutions of a group of different functions that develop serially, beginning at different age epochs, reaching their maximum vigor, and then declining. The hyaline cartilage dies of old age when bone is formed of it, as the milk teeth do. The thymus gland has completed its growth at the third year and slowly atrophies with every sign of age. The nervous system has the most sustained evolution. The infant, child, youth, are learning higher coördinations, and the psycho-motor system is not completely evolved till the end of the teens. The hand and arm centers continue their development and do not attain their perfection before thirty. The writer studied workmen in various factories and found that in many cases proficiency in manipulation grew for a decade and then became stationary at thirty, beyond which it could never be increased, and later declined. This decline took place sooner in highly specialized than it did in more general movements. In some artists, however, manual skill may increase to a great age.

In the brain centers that preside over language there is continuous development, so that it has been carefully estimated that our powers of expression culminate between 45 and 55. Demosthenes’ De Corona, his masterpiece, was delivered at the age of 52; Burke’s impeachment of Hastings, when he was 58; and many authors have thought their vocabulary and command of language at its best during this decade. After this, faint symptoms of aphasia and amnesia begin to show themselves. But it is in the frontal lobes, in which it is now believed that the powers of attention, reason and judgment are located, that the acme of development comes still later, perhaps in the decade ending at the age of 65. Indeed, Moebius and others have shown that the cortical layers believed to be most closely associated with mentation are still developing as late as the age of sixty-three. Bacon produced the first two books of the Novum Organum at 59; Kant’s Critique of Pure Reason was produced when he was 57; Harvey’s great work on the circulation, when he was 72, etc. It is certain that long after memory of names and physical vigor have begun to abate, the power of comparison, inference, and above all a moral sense, which is perhaps the finest and latest of all our powers, comes to full maturity.

The ideal of a greater old age is not an idle dream and Browne insists that physicians should strive themselves to live to be 100 and to make their patients do so. The best antiseptic against senile decay is, he thinks, active interest in human affairs. This, at any rate, should be our working hypothesis. A man of 80 should realize that he has one-fifth of his life before him. He tells us of a man of 84 who attempted suicide because he could no longer support his parents, and of another of 102 who had undergone a successful operation for cancer of the lip without anæsthetics. Of course, senile involution, when cell growth is more than counterbalanced by cell decay, is the natural pathway to death, and a man ultimately dies of it when there is no question of disease. But the brain, like the lens of the eye, may become flatter and more longsighted, focusing better on objects far than those that are near. There is no short cut to longevity. Its achievement must be the work of a lifetime. Sympathy, which goes far deeper than courteous manners, is fundamental for the successful treatment of old age.

H. M. Friedman[146] begins his comprehensive treatise with biological and embryological considerations, and here perhaps he makes his most original suggestions. The higher the plane of the animal, the more marked is cell differentiation or specialization and this affects most cells. Once a degree of differentiation is observed, no backward step to a previous state of generalization, regeneration, or rejuvenation is possible. The higher the ascent of the cell in the plane of differentiation, the lower is its power of rejuvenation. Connective tissue, muscle fiber, and cylindrical cells are the least differentiated and therefore have the greatest power of regeneration. Nerve cells have the least because their work is of a high order and they are most specialized. Nerve fibers are mere conductors and they and epithelial cells have probably the greatest power of regeneration.

Again, the more differentiated the cell, the more rapid is its development, early decline, and death. Precocity even of the separate cell purports early maturity. “So senescence is an increased differentiation of the protoplasm, while rejuvenation is an increase of the nuclear elements at the expense of the protoplasm.” The increase of nuclear material allows fission and the formation of new cells. Thus the degree of differentiation is greatest as fission or mytosis is least. The power of regeneration is in direct proportion to the power of cell fission. Thus “the greater the cell differentiation, the smaller the mytotic index.” With maturity the decrease of the mytotic index, or the number of tissues into the composition of which the cell can enter, becomes restricted. The cells in the original germinal layer have before them the possibility of entering into the structure of any tissue, but as cells differentiate the germinal layers take on a more structural character and leave the field to the entrance of cells into different tissue formations more restricted, since during development the number of tissues yet unformed or undifferentiated becomes less and less and once a cell has assumed a personality it must continue to follow it up and cannot diverge from it. This is the law of genetic restriction. The younger the cells, the greater their multiplying power and the greater the tissue possibilities they can choose. Hence morbid tumors are formed from young cells of higher mytotic index whose genetic restriction has not progressed far enough to inhibit range and rapidity of growth. Before genetic restriction young cells may become one tissue or another. Injuries causing cell degeneration of the young cells are often, therefore, the seats of morbid growths. The young or undifferentiated cells forming malignant amorphous tumors and growing in tissues alien to them develop rapidly, probably because they are deprived of the “social” restriction to overgrowth that they would have in their own cell society. Thus the presence of young cells in out-of-the-way places or where older and more differentiated cells would be expected should excite suspicion. “Young cells, like young children, are safest among their own.”

Generally a cell in an organism lives long enough to reproduce its kind; else the species would die and death does occur in many lower organisms immediately after ovulation. The young thus grow rapidly, while old age is the period of slowest growth; and indeed the rate of growth depends upon the degree of senescence. The tendency to senescence is at its maximum in the very young and the rate of senescence diminishes with age.

As to the cause of senility, physiologically it is desiccation. At birth there is most fluid and gaseous material, but organization demands solidarity. Lactic acid may retard the growth of intestinal flora and the up-keep of the intestinal toilet by larvage. Intoxication of some kind is a factor in many of the changes accompanying senility. Lorand thought age was chiefly due to atrophy and degenerative tissue by failure of the function of the ductless glands, especially the thyroid. The myxedematous look and are old. Thus the limit of life is a matter of excretion. The special organs of elimination cannot act to their full capacity or to that of vital necessity because of the replacement in senility of parenchyma by fibrous or fatty tissue. The retained waste products increase the sclerotic changes and produce a vicious circle—irritation, intoxication, and atheroma. The degeneration of the first stage produces insufficiency of the organs of elimination and the degeneration of all organs.

As to physical manifestations, there is atrophy of the higher and more specialized cells and they are replaced by hypertrophied connective tissue. The heart is enlarged but this is compensatory for the stiffening and narrowing of the lumen of the great vessels near it and so the blood pressure is increased. The changes in bone, ligament, and tendons are extreme, with increased enervation throughout the body and perhaps senile marasmus, which may bring extreme emaciation or osteomalacia and even bone deformity. This may affect nervous and mental elements, like senile asystole and changes in the blood. The temperature, however, is not affected.