Seventy is, on the whole, the most dangerous milestone and the morning of that birthday is probably the saddest of all that those who attain it have known or will ever know. It brings a new consciousness that now indeed we are old; and if we still carry on as before, we are at least under the suspicion of affecting a vigor that we really lack and are liable to lapse to an apologetic state of mind because we do not step aside and give our place to our juniors who often feel that they have a right to it, even though they try not to show or even confess it to themselves. If we make partial withdrawal we find insistencies, conscious and unconscious, in those who supersede us that we might as well make it complete and the sense of being superfluous and no longer needed is bitter. Complete retirement from all our life work, whatever it is, may make us feel that we are already dead so far as our further usefulness is concerned. Yet at no stage of life do we want more to be of service than when we are deprived of our most wonted opportunities to be so. We do not take with entire kindness and resignation to being set off as a class apart. CHAPTER VI THE CONTRIBUTIONS OF BIOLOGY AND PHYSIOLOGY Weismann’s immortality of the germ plasm and his denial of the inheritance of acquired qualities--The truth and limitations of his views--The theories of Hering and Simon--Metchnikoff’s conception of the disharmonies in man, of the rôle of intestinal flora and their products, of euthanasia, and of the means and effects of prolonging life--C. S. Minot’s conception of the progressive arrest of life from birth on as measured by declining rate of growth and his neglect to consider the dynamic elements--C. M. Child’s studies of rejuvenation in lower and higher forms of life in the light of the problems of senescence--J. Loeb’s studies of the effects of lower temperatures, of toxins, and ferments--The preservation of cells of somatic tissues potentially immortal under artificial conditions--Account of the studies of Carrel, Pozzi, and others--Investigations upon the effects on sex qualities and age of the extracts and transplantations of glands, from Claude Bernard--Investigations of Eugene Steinach on the interchange of sex qualities and rejuvenation by glandular operations in animals and man--G. F. Lydston’s work--Serge Voronoff’s experiments and his exposition of the achievements and hopes of glandular therapy--Some general considerations in view of work in this field.