La Bruyère expresses it in an apothegm, "We want to grow old, and we fear old age." One would like longevity without old age.
But can life be prolonged without senility diminishing its value? Metchnikoff thinks it can. He more or less clearly catches a glimpse of a normal evolution of existence which would make it longer and nevertheless exempt from senile decay.
It is remarkable that we have so few scientific data on the old age of man, and we have still fewer on that of animals. The biologist knows no more than the layman. The old age of the dog is betrayed by its gait. Its coat loses its lustre, just as in disease. The hair whitens around the forehead and the muzzle. The teeth grow blunt and drop out. The character loses its gaiety and becomes gloomy; the animal becomes indifferent. He ceases to bark, and often becomes blind and deaf.
It is admitted that senile degeneration is due to an alteration affecting most of the tissues. The cells, the special anatomical elements of the liver, the kidney, and the brain are reduced by atrophy and degeneration. At the same time, the conjunctive woof which serves them as a support develops, on the contrary, at the expense in a measure of the higher elements. For this reason the tissues harden. We know that the flesh of old animals is tough. We know in pathology that this is happening to the tissues. It is due to growth, to injury to the active and important elements, to the elements of support of the organs. They form a tissue sometimes called packed tissue, to show its secondary rôle with reference to the elements which are deposited in it. This kind of degeneration of the organs is
