Elie Metchnikoff, sub-director of the Pasteur Institute of Paris, is a philosopher, as well as a physiologist; a philosopher who brings to the support of his speculations the exact methods of the laboratory. He, with the other great leaders of the new art of health, is at last removing from science the reproach leveled at it by Metchnikoff’s great fellow-country-man and friend, Tolstoi, who said that science was useless to man, since it did not direct its attention to the problems which mean most to humanity, such as the great questions of life and death, but confined its efforts to investigating useless birds and butterflies. [Illustration: M. ELIE METCHNIKOFF, OF THE PASTEUR INSTITUTE OF PARIS. His researches have thrown great light on autointoxication. He believes that the normal life should be over 125 years long.] The books in which Metchnikoff has recorded the results of the investigations which for many years he has been making into the problems of old age and death, have caused a profound sensation in the scientific world. In these books, the great Russian emphatically and definitely ranks himself with the optimists. He states that scientific study of the constitution of man, and of the workings of man’s nature, and of his environment in the world, do not support the view that man is born unto sorrow as the sparks fly upward—to quote the words of the Psalmist—but can really be fitted to live a useful and happy life, ending in a calm and peaceful old age—if man will but turn his attention to the knowledge by which he can really live in harmony with his environment. Metchnikoff has arrived at the conclusions that man and woman would live to be at least one hundred years old, if they could enable their bodies to eliminate those deadly toxins which are the product of the activities of the bacteria which inhabit the human body, as well as of the body’s own organic processes. Age is not always to be computed in years. As a common saying puts the case, “A man is as old as he feels, a woman as old as she looks.” A famous French physiologist has altered this to read, “A man is as old as his arteries.” The primary change produced by the coming of old age is the hardening and withering of the arteries. As the result of this withering process, a large number of the smaller arteries disappear, so that the blood supply of the muscles, brain, heart, and other important organs, is cut off. This is the change that is technically known as “arterio-sclerosis.” It is quite often found in persons of less than fifty years of age. On the other hand, Harvey, the famous discoverer of the circulation of the blood, declared that in the post-mortem examination made of Old Parr, the celebrated Englishman who died at the age of one hundred and fifty-two years and nine months, he found not a trace of this degenerative change.