based upon experiment. The transformation has opened out an illimitable vista of possibilities in the direction not only of cure, but, more important still, of prevention. It has taken place within the memory of most of us who are here present. And only last February the world was mourning the death of one of the greatest of its benefactors—a former president of this association '-who, by applying this knowledge to the practice of surgery, was instrumental, even in his own lifetime, in saving more lives than were destroyed in all the bloody wars of the nineteenth century!

SENESCENCE AND DEATH.

The question has been debated whether, if all accidental modes of destruction of the life of the cells could be eliminated, there would remain a possibility of individual cell life, and even of aggregate cell life, continuing indefinitely; in other words, Are the phenomena of senescence and death a natural and necessary sequence to the existence of life? To most of my audience it will appear that the subject is not open to debate. But some physiologists (e. g., Metchnikoff) hold that the condition of senescence is itself abnormal; that old age is a form of disease or is due to disease, and, theoretically at least, is capable of being eliminated. We have already seen that individual cell life, such as that of the white blood corpuscles and of the cells of many tissues, can under suitable conditions be prolonged for days or weeks or months after general death. Unicellular organisms kept under suitable conditions of nutrition have been observed to carry on their functions normally for prolonged periods and to show no degeneration such as would accompany senescence. They give rise by division to others of the same kind, which also, under favorable conditions, continue to live, to all appearance indefinitely. But these instances, although they indicate that in the simplest forms of organization existence may be greatly extended without signs of decay, do not furnish conclusive evidence of indefinite prolongation of life. Most of the cells which constitute the body, after a period of growth and activity, sometimes more, sometimes less prolonged, eventually undergo atrophy and cease to perform satisfactorily the functions which are allotted to them. And when we consider the body as a whole, we find that in every case the life of the aggregate consists of a definite cycle of changes which, after passing through the stages of growth and maturity, always leads to senescence, and finally terminates in death. The only exception is in the reproductive cells, in which the processes of maturation and fertilization result in rejuvenescence, so that instead of the usual downward change toward senescence, the fertilized ovum obtains a new lease of life, which is carried on into the new-formed organism. The latter

1 Lord Lister was president at Liverpool in 1896.

again itself ultimately forms reproductive cells, and thus the life of the species is continued. It is only in the sense of its propagation in this way from one generation to another that we can speak of the indefinite continuance of life; we can only be immortal through our descendants!

AVERAGE DURATION OF LIFE AND POSSIBILITY OF ITS PROLONGATION.

The individuals of every species of animal appear to have an average duration of existence.1 Some species are known the individuals of which live only for a few hours, whilst others survive for a hundred years. In man himself the average length of life would probably be greater than the three-score and ten years allotted to him by the Psalmist if we could eliminate the results of disease and accident; when these results are included it falls far short of that period. If the terms of life given in the purely mythological part of the Old Testament were credible, man would in the early stages of his history have possessed a remarkable power of resisting age and disease. But, although many here present were brought up to believe in their literal veracity, such records are no longer accepted even by the most orthodox of theologians, and the nine hundred odd years with which Adam and his immediate descendants are credited, culminating in the 969 of Methuselah, have been relegated, with the account of Creation and the Deluge, to their proper position in literature. When we come to the Hebrew Patriarchs, we notice a considerable diminution to have taken place in what the insurance officers term the "expectation of life." Abraham is described as having lived only to 175 years, Joseph and Joshua to 110, Moses to 120; even at that age "his eye was not dim nor his natural force abated." We can not say that under ideal conditions all these terms are impossible; indeed, Metchnikoff is disposed to regard them as probable; for great ages are still occasionally recorded, although it is doubtful if any as considerable as these are ever substantiated. That the expectation of life was better then than now would be inferred from the apologetic tone adopted by Jacob when questioned by Pharaoh as to his age: "The days of the years of my pilgrimage are an hundred and thirty years; few and evil have the days of the years of my life been, and have not attained unto the days of the years of the life of my fathers in the days of their pilgrimage." David, to whom, before the advent of the modern statistician, we owe the idea that 70 years is to be regarded as the normal period of life,3

1 This was regarded by Buffon as related to the period of growth, but the ratio is certainly not constant. The subject is discussed by Ray Lankester in an early work, On Comparative Longevity in Man and Animals, 1870.

The approximately regular periods of longevity of different species of animals furnishes a strong argument against the theory that the decay of old age is an accidental phenomenon, comparable with disease. The expectation of life of a healthy man of 50 is still reckoned at about 20 years.

is himself merely stated to have "died in a good old age. The periods recorded for the Kings show a considerable falling off as compared with the Patriarchs; but not a few were cut off by violent deaths, and many lived lives which were not ideal. Amongst eminent Greeks and Romans few very long lives are recorded, and the same is true of historical persons in medieval and modern history. It is a long life that lasts much beyond 80; three such linked together carry us far back into history. Mankind is in this respect more favored than most mammals, although a few of these surpass the period of man's existence.1 Strange that the brevity of human life should be a favorite theme of preacher and poet when the actual term of his "erring pilgrimage" is greater than that of most of his fellow creatures.

THE END OF LIFE.

The modern applications of the principles of preventive medicine and hygiene are no doubt operating to lengthen the average life. But even if the ravages of disease could be altogether eliminated, it is certain that at any rate the fixed cells of our body must eventually grow old and ultimately cease to function; when this happens to cells which are essential to the life of the organism, general death must result. This will always remain the universal law, from which there is no escape. "All that lives must die, passing through nature to eternity."

Such natural death unaccelerated by disease is not death by disease as unnatural as death by accident? should be a quiet, painless phenomenon, unattended by violent change. As Dastre expresses it, "The need of death should appear at the end of life, just as the need of sleep appears at the end of the day." The change has been led gradually up to by an orderly succession of phases, and is itself the last manifestation of life. Were we all certain of a quiet passing were we sure that there would be "no moaning of the bar when we go out to sea"-we could anticipate the coming of death after a ripe old age without apprehension. And if ever the time shall arrive when man will have learned to regard this change as a simple physiological process, as natural as the oncoming of sleep, the approach of the fatal shears will be as generally welcomed as it is now abhorred. Such a day is still distant; we can hardly say that its dawning is visible. Let us at least hope that, in the manner depicted by Dürer in his well-known etching, the sunshine which science irradiates may eventually put to flight the melancholy which hovers, batlike, over the termination of our lives, and which even the anticipation of a future happier existence has not hitherto succeeded in dispersing.

1"Hominis ævum cæterorum animalium omnium superat præter admodum paucorum."-Francis Bacon, Historia vitæ et mortis, 1637.

THE ORIGIN OF LIFE: A CHEMIST'S FANTASY.1

By H. E. ARMSTRONG.

"Behold, the beginning of philosophy is the observation of how men contradict each other and the search whence cometh this contradiction and the censure and mistrust of bare opinion. And it is an inquiry into that which seems, whether it rightly seems; and the discovery of a certain rule, even as we have found a balance for weights and a plumb-line for straight and crooked. This is the beginning of philosophy."-EPICTETUS.

The presidential address delivered recently to the British Association at Dundee by Prof. Schäfer and the subsequent independent discussion, at a joint sitting of the physiological and zoological sections of the Association, of the subject considered in the president's discourse will at least have served as a corrective to the wave of vitalism that has passed over society of late years, owing to the pervasive eloquence of Bergson and other writers who have elected to discuss the problems of life, mainly from the metaphysical and psychological points of view, with little reference to the knowledge gained by experimental inquiry.

As Prof. Schäfer himself remarked, the problem of the origin of life is at root a chemical problem. It is somewhat surprising, therefore, that the chemists were not invited to join in the debate at Dundee. Judging from the remarks that fell from several of the speakers, their sobering presence was by no means unnecessary. It is clear that, so long as biologists are satisfied with the modicum of chemistry which is now held to serve their purpose, they will never be able to escape from the region of vague surmise.

On the Tuesday Prof. Macallum fancifully pictured the earth as at one time "a gigantic laboratory where there had been a play of tremendous forces, notably electricity, which might have produced millions of times organisms that survived but a few hours, but in which also, by a favorable conjunction of those forces, what we now call life might have come into existence." I think I heard him then refer to the great stores of oil we now possess and imply that they

1 Reprinted by permission from Science Progress in the Twentieth Century, No. 26, October, 1912. London, pp. 312-329.