The background view of the work in Voronoff’s field, roughly stated, is as follows. Somatic cells, having lost the power to propagate the whole body, as they develop and multiply become more and more special, not only in form but in function, until they finally lose the power of multiplication or of regeneration. These are higher and perform the most particularized functions. Besides these most individualized cells, so characteristic of every organ that a cytologist can at once distinguish cells that form the epithelium, intestines, brain, muscle, glands, etc., there always remain other far less differentiated or more primitive cells, chiefly leucocytes or white blood corpuscles and the connective tissue cells. The former float in the blood and can pass out through the thin walls of the capillaries into other tissues. The latter constitute all the firmer supportive framework of every organ. They are very robust, fecund proletarians and are largely made up of the former. From birth they wage unceasing war upon the nobler, more professional and expert, but less independent cells which have sacrificed most of their cruder, pristine powers for service to the body corporate. These higher cells represent the extreme division of labor within our bodies. They are no longer sufficient unto themselves but each class of them depends upon the work of others. The low, banal, barbaric but vigorous cells of the conjunctive tissue, on the other hand, always strive to destroy and to themselves take the place of the higher cells and it is this process slowly going on everywhere that constitutes old age and all its processes of hardening, atrophy, disintegration, etc., for these lower cells cannot discharge the functions of the higher ones they have supplanted and hence comes anarchy within the organ or body. We die because nature tends so strongly to develop the cruder type of cell that makes up the connective tissue.