The Darwin celebration at Cambridge, in June 1909, brought a wonderful assemblage of celebrated biologists from all parts of the world to this country. There never has been seen such a company of great discoverers of all nationalities in the field of natural history and the science of living things, as were present in the University of Cambridge during that week. Even philosophers, moralists, and jurists were present to join with the one great political leader of our own country who really knows and appreciates the importance of the scientific study of Nature—the Right Hon. Arthur J. Balfour—in his fervent and heartfelt tribute to the influence of Darwin’s work and theory in all departments of human knowledge, thought, and activity. One of the most remarkable men present was Elie Metchnikoff. He represented both Russia, the country of his birth and earlier scientific work, and his adopted country, France, where, as sub-director of the Institut Pasteur, his later and most important researches have been carried on. Russia was also represented by Salensky, late director of the Museum of St. Petersburg, well known to us all as a discoverer in the embryology (growth from the egg) of marine animals, and by Timiriazeff, the botanist, renowned for his work on the mode in which leaf-green or “chlorophyll” enables green plants to obtain their food from the gases of the atmosphere. France had other representatives in Edmond Perrier, director of the Paris Museum, and Prince Roland Bonaparte.

Metchnikoff was one of the four representatives selected by the University to deliver orations in the Senate House in honour of Darwin. He especially drew attention to the influence of Darwin’s theory on the study of disease. The recognition of the derivation of man from animal ancestors, and of the complete community of the structure and the chemical activity of the organs of man with those of the organs of animals, had made (he said) the study of the diseases of animals a necessary feature in the understanding of the diseases of man. The far-reaching principle of Darwin that the mechanisms and processes observed in the bodies of plants and of animals (including man) must have been selected in the struggle for existence and perpetuated, because of their utility, led Metchnikoff to inquire what is the value or use of the process called inflammation and of the “eating corpuscles,” or “phagocytes” (so named by him), which wander from the blood into inflamed tissues. This question had led him to the discovery that the phagocytes engulf and destroy disease-germs, and are the great protectors of the animal and human body against bacteria and other germs which enter cut and wounded surfaces, and would start disease were there not “inflammation,” which is nothing more nor less than a nerve-regulated stagnation of the circulation of the blood at the wounded spot, and the consequent arrival at this spot of thousands of “phagocytes,” which pass out of the stagnant blood through the walls of the fine blood-vessels. These armies of phagocytes proceed to eat up and destroy all the germs which fall on to the wound—from the air, from dirty surfaces, and from the skin. The utility of inflammation and its gradual development, according to Darwinian principles, in the animal series, was shown twenty years ago by Metchnikoff. His important work on “immunity” and on infection and on protection against germ-caused disease is thus seen to be one of the many flourishing and valuable branches of knowledge which have originated from Darwin’s great conception and his example in experiment and inquiry.

Metchnikoff is now devoting all his attention to the possibility of prolonging human life. The facts seem to show that if we ate and drank only what is best for us, and led lives regulated by reason and knowledge, we should, nearly all, attain to 80 or even 100 years of age, having healthy minds and healthy bodies. We should die quietly and comfortably at the end, with much the same feeling of contentment in well-earned final repose as that which we now experience in going to sleep at the end of a long and happy day of healthy exercise and activity. Metchnikoff thinks that the causes of too early death may be ascertained, and when ascertained avoided or removed. In 1870, in a little book on Comparative Longevity, I distinguished what we may call the “possible life,” or “potential longevity,” of any given human being from his or her “expectation” of life. Potential longevity has been well called our “lease” of life. It is probably not very different in different races of men or individuals, and is probably higher than King David thought, being 100 to 120 years, and not merely 70 years. We all, or nearly all, fail to last out our “lease” owing to accidents, violence, and avoidable, as well as unavoidable, disease; so that 70 years is named as our tenure when the injury done to us by unhealthy modes of life and by actual disease are considered as inevitable. Metchnikoff proposes to discover and to avoid those conditions which “wear down” most of us and produce “senility” and “death” before we have really run out our lease of life.

Human beings die most abundantly in the earliest years of life. Statistics show that at birth the chance or expectation of life is only 45 years, whilst at 10 years old you may expect to live to be 61. At 30 you have not a much better chance—you will probably, if you are what is called a “healthy” life, die when you are 65. But if you survive to be 50 you may expect, if you have not any obvious disease or signs of “break up,” another twenty years, and will probably die at 70; surviving to 60, you may expect, if you are what passes for “healthy,” to live to 73. Now, it is especially with regard to life after 40 or 50 years of age that Metchnikoff is interested. Those who have survived the special dangers and difficulties of youth, and have arrived at this mature age, ought to be able to realise much more frequently than they do something like the full “lease of life.” There seems to be no reason why they should not avoid the usual rapid “senile changes” or weakness of old age, and survive, as a few actually do, to something like 100. The causes of “senile change” and the way to defeat their operation are what Metchnikoff is studying. Hardening of the walls of the arteries set up by certain avoidable diseases contracted in earlier life, and by the use of alcohol (not only to the degree which we call “drunkenness,” but to such a degree as to make one depend on it as a “pick-me-up”), is an undoubted cause of that weakness and liability to succumb to other diseases which is so general after 50 years of age. The causes which produce hardened arteries can be avoided. Another cause of senile changes is declared by Metchnikoff, to arise from the continual absorption of poisonous substances produced by the decomposition of partially digested food in the lower bowel or large intestine. This is at present the chief subject of his study. It is to prevent the formation of these poisons that he has introduced the use of sour milk, prepared with the lactic ferment. Since the Cambridge celebration he has been in London in order to examine the condition of certain patients from whom a distinguished English surgeon has found it necessary to remove the “large intestine.” Metchnikoff wishes to ascertain what bacteria, poison-producing or other, are present in these patients, and what is their general chemical condition now that this poison-producing part of the digestive canal has been taken from them.

In Paris, Metchnikoff has some very interesting experiments in progress with bats. He uses the large tropical fruit-eating bats, or “flying foxes.” They have a very short intestine, and very few bacteria and of very few kinds are to be found in its contents. On the other hand, there are as many as thirty distinct kinds of bacteria producing putrefaction or other chemical change in the digestive canal of man—and their quantity is gigantic. They pervade the whole contents of the human digestive canal by millions. By properly feeding the flying foxes in his laboratory in Paris Metchnikoff has actually succeeded in getting rid of all bacteria from their digestive canal, so that he now has adult mammalian animals, not very remote from man in their structure, food, and internal chemistry, which are absolutely free from the intestinal parasitic bacteria which he supposes to cause poisoning and senile changes in man. It is obvious, without pursuing the matter into further detail here, that Metchnikoff is now in a position to test his views as to the action of particular kinds of bacteria—he has animals which are free from them. He can make an experiment, keeping some of his bats still free from bacteria and causing some to be largely infected by this or that kind, and he can compare the result in regard to the health and chemical condition of the animals. So, too, the patients from whom the lower intestine has been removed may very probably furnish him (through his assistant who remains in London) with important facts for comparison with the condition of persons who have not been deprived of this part of the digestive apparatus.

I have given this sketch of what my friend is doing in order to furnish some notion of the kind of investigation which he pursues. He does not expect to extend the “lease” of human life, but by ascertaining in a definite scientific way the true rules of internal and external “hygiene” he does hope to give mankind an increased “expectation” of life; in fact, to enable a vastly larger number of men and women to enjoy that lease to the full, and to die without disappointment and regret, even with contentment and pleasure, at the end of it.

Metchnikoff was in Russia in the spring of 1909, and spent a day with Tolstoi. They were “fÊted” and photographed together, the greatest artist and the greatest scientist of Russia. Tolstoi is 81 years of age. He took Metchnikoff out alone for a drive in his pony-cart so as to talk with him without interruption. “What do you think of life?” was the first question he asked, and one which it took my friend some time to answer. In regard to vegetarianism the two great men did not agree. When Metchnikoff declared that there was less cruelty on man’s part in killing wild animals to eat them than in leaving them to die by the tooth and claw of predaceous animals or from starvation, Tolstoi observed that that was argument and reason, and that he paid no attention to them; he only guided himself (he said) by sentiment, which he felt sure told him what was good and right! He was, however, deeply interested in an account of the cannibalism of savage races of men, concerning which he seemed to be quite uninformed. He also was profoundly interested in Metchnikoff’s view that Goethe, in the second part of Faust, is chiefly bent upon depicting the persistence of the amorous passion in old age—of which Goethe himself was an example—and Tolstoi declared that this gave a new meaning to the poem, which he had always hitherto found dull and unintelligible. But when Metchnikoff described in glowing words the joy and even rapture with which man will hereafter welcome the repose and mystery of death, having completed a long and healthy life of some hundred years, Tolstoi declared that this was indeed a fine conception, although it was entirely subversive of his own notions as to the significance of life and death. Tolstoi also stated that he had written his stories rapidly and without effort, but that his essays on morality and religion had cost him great labour; and, further, that he could not now remember the former, though the latter still were developing and incessantly occupied his thought.

It was admitted with regret by Darwin that he ceased in middle age to care for poetry and art, though there seems to be no doubt that he mistook fatigue and preoccupation of mind for a real change in taste and power of appreciation. It is interesting to place beside this the case of the great literary artist, Tolstoi, who not only frankly confesses that he refuses to be guided by reason and follows sentiment, but is also profoundly ignorant upon all the most ordinary topics of human life outside his own village, and of all Nature and her workings. Would Tolstoi have been a greater or a smaller artist if he had had a larger knowledge of the things that are? Was Darwin’s great scientific achievement really related to an innate indifference to what is called “poetry”? I will not now discuss the matter, but I am convinced that so far as natural gift is concerned, the keenest scientific capacity is not only compatible with the fullest sensibility to art and with the power of poetical vision and expression, but is often accompanied by them; and, further, that the work of an artist, if he is a great artist, cannot be hampered by knowledge. It is only the small talent or the feeble genius that can be paralysed rather than developed by the fullest experience and the widest knowledge. Necessary incompatibility of mental qualities has no place in this matter; what has led to the erroneous assumption that it has, is the excessive exercise by exceptional individuals of certain powers—a specialism necessary for effort and success, but deliberately chosen, and not due to an inborn one-sidedness.