After some weeks the sluggish currents of being in the rat, which had slowed down as a preliminary to stopping altogether, flow fast and furious. Waves of new chemical substances inundate his cells. And they respond like the fields that border the Nile after the annual flood. All his tissues, skin, muscle, nerve, even bone, are restored. A vitality is created which makes him bound and dart like a youth of his species. In due time, though, senility returns. It is as if a storage battery, recharged, runs down and becomes dead again. Slitting the genital duct of the other testis, causing its interstitial cells to hypertrophy and multiply, repeats the effects of the first experiment. The organism responds again to the new waves of vitality that vibrate through it. That it is recharged is demonstrated again by a revival of sex appetite and sex activity. The female which had become an object of indifference is reinstated as a creature to be sought and pursued. The second period ends in its turn. And now entirely new interstitial glands, in the form of fresh testes removed from a young animal, are transplanted into the body of the old rat. Once more youth returns. But now it burns itself more quickly than even before. An acute exhaustion of the mind appears first. Then all the other phenomena of old age steal back upon the old rat, and senility, firmly established in the saddle, rides him to the end.
THE POSSIBILITIES OF REJUVENATION
Whatever other deductions may be extracted from these experiments, they prove beyond a doubt the existence of an endocrine factor in the process of aging, as well as an arterial. They also demonstrate that the internal secretion of the sex glands, well advertised as it has been as the Elixir of Youth that Ponce de Leon, and Brown-Séquard with so many others, pursued in vain, is not the whole story. For if it was, the duration of the new youth should be another span of life, whereas in actuality it is only a fraction of that time. This fact, together with a number of others, make clear that while the gonads may be the jeune premier of the drama, the vitality of the plot depends upon the other endocrines. Since old age is an exhaustion, permanent and irreparable of all the members of the ductless gland directorate, the reason becomes clear for the temporary quality of the rejuvenation effected by the procedures of Steinach.
Practically, then, the question at once arises: which of the glands in particular are involved? There is first that ubiquitous agent in the system, the thyroid. Chemical analysis of it has shown that the iodine content decreases with the age of the individual, and becomes specially low after forty. It is after the menopause in women that myxedema, the disease of complete degeneration of the thyroid, and of the physical and mental faculties, is most frequent. The thyroid of old people exhibits, in varying degrees, signs of a similar degeneration. Thyroid feeding, properly controlled, will clear up certain of the deteriorations of mind and body observable in the aged. The grossness of the features lessens, a number of the pains go, muscular endurance increases, memory and intelligence do not remind one so forcibly of the old dotard in his second childhood. Of course the improvement at present achievable is only relative. But in the prematurely aging, decay invading a half accomplished maturity, marvels have been achieved at times with feeding of the gland.
The pituitary, too, begins to retrogress after the period of maturity. And an early retrogression means a short maturity. In women, the onset of an obesity, and coincidently, of a lazy and dull morale, coincides with this declension of the pituitary powers. All the glands of internal secretion, in fact, shrink and shrivel as old age advances. Only, as in other relationships, the predominating endocrine stamps its signature more visibly upon the documents of decadence than the others. Pituitary types, as said, get fat and slow, thyroidal become bulky and stupid or thin and sour, the adrenal dark, shrunken and forever tired of life. So type emerges, even in all-around glandular deficiency.
The problem of rejuvenation is the problem of recharging, or replacing all of the glands of internal secretion, at least the most important, the thyroid, the pituitary and the adrenals, as well as the gonads. Longevity is perhaps largely a matter of preventing, or postponing their wane. Beside, there is the prophylaxis of bacterial infections, and their all embracing corrosions—which, too, have an endocrine aspect.
Persistence of youth or juvenility may be manufactured by nature in two ways. There may be a persistence of early glandular predominances. We have seen what happens to the thymocentric. That a pineal-centered juvenile or infantile type exists may be safely predicted. Nature's only other mode of securing perpetual youth seems to be by prolonging the time allotted to the sex gland crescendo.
As for the golden age of maturity itself, what humdrum people and poets have despised as middle age, the margin of reserve of the ruling hormone is a quantity almost malleable in our hands, but still to be regarded with respect as a hard cold proposition by the physiologist. In general, the continuance of any stage of development means the maintaining of the glandular administration peculiar to it. So the chubby debonair irresponsible whom nothing can touch is happy in the possession of a pineal uncorrupted by the years, while the genius who can turn out his best work at sixty-five must thank his pituitary for standing by him to the end.
THE SCIENCE OF PUERICULTURE
There is a specialty now growing in the womb of science which in its own good time will come to fruition as the study of the child's needs or puericulture. Even today there exists a scientific basis for the formulation of the principles upon which every child should be brought up. Though we have had marvelous results from the campaigns to lower infantile mortality, most of what has been done has been medical in its interest, and so largely negative in its accomplishments. The removal of the causes of evil no doubt gives the good its opportunity. But how to raise a child, endowed with satisfactory ancestral stuff, as a Grade A normal or supernormal, still remains to be erected into an exact science.