Page:Popular Science Monthly Volume 70.djvu/494

490 Pasteur Institute in Paris, some of whose publications many of you have doubtless read, that his conception of the nature of senility, of old age, could best be expressed in a single word, atrophy. "On résume la senilité par un seul mot: atrophie." That is his estimate of old age. But that is not the only estimate of old age which has been made up to the present time. We find one, which is much more prevalent, is that which connects it with the condition of the arteries. Indeed, Professor Osier has written this sentence—"Longevity is a vascular question, and has been well expressed in the axiom that a man is only as old as his arteries." Now these are medical views, not biological, and you will find that there is a very extensive literature dealing with old age in man based upon the conception that old age is a kind of disease, a chronic disease, an incurable disease. Medical writers have put forward various conceptions giving a medical interpretation of this disease. That to which I just referred is the favorite one, the one you are most likely to hear from physicians to-day—namely, the theory of arterial sclerosis, that the hardening of the walls of the arteries is the primary thing; it interferes with the circulation, the bad circulation interferes with the proper working of every part of the body, and as the circulation becomes impeded, various accessory results are produced in the body in consequence. It is brought to a lower or more diseased condition than before. And so they interpret sclerosis of the arteries as the primary thing, because they can trace so many alterations in the old which resemble diseased alterations, to these natural changes in the arteries by which they acquire hardened and inelastic walls, which prevent the proper response of the artery to the heart beat, upon which the normal healthy circulation largely depends. Another interpretation, very curious and interesting, is that which has been recently offered by the same Professor Metchnikoff whom I have just mentioned. He has written a book upon the 'Nature of Man,' translated in 1903, and published in this country. It is an interesting book. It gives a most attractive picture, incidentally, of Metchnikoff himself, a man of pleasantly optimistic temperament, but a man thoroughly imbued with the spirit which has so often been attributed to contemporary scientific men, of cold, intellectual regard towards everything, towards life, towards man, towards mystery. For him mysteries of all sorts have little interest. Those things which are mysterious are beyond the sphere of what can hold his attention. He must reside in the clear atmosphere of definite, positive fact. This mental bias is shown in his book. He reviews in a happy way various past systems of philosophy; he describes various religions; and he points out his reasons for thinking that all of these are insufficient, that there is no satisfaction to be derived from any of the ancient