[25] While this has been demonstrated thus far only for connective-tissue cells it may be true also for other cells. This effect of lack of oxygen explains also why the immortality of the somatic cells is not obvious. Death in a human being consists in the stopping of heart beat and respiration, which also terminates the action of the brain or at least of consciousness. Immediately after the cessation of heart beat and respiration the cells of muscle and of the skin and probably many or most other organs are still alive and might continue to live if transferred to another body with circulation and respiration. As a consequence of the lack of oxygen supply in the dead body they will, however, die comparatively rapidly. It may be stated that hearts taken out of the body after a number of hours can still beat again when put into the proper solutions and upon receiving an adequate oxygen supply. The idea that the body cells are naturally immortal and die only if exposed to extreme injuries such as prolonged lack of oxygen or too high a temperature helps to make one problem more intelligible. The medical student, who for the first time realizes that life depends upon that one organ, the heart, doing its duty incessantly for the seventy years or so allotted to man, is amazed at the precariousness of our existence. It seems indeed uncanny that so delicate a mechanism should function so regularly for so many years. The mysticism connected with this and other phenomena of adaptation would disappear if we could be certain that all cells are really immortal and that the fact which demands an explanation is not the continued activity but the cessation of activity in death. Thus we see that the idea of the immortality of the body cell if it can be generalized may be destined to become one of the main supports for a complete physicochemical analysis of life phenomena since it makes the durability of organisms intelligible. 5. This generalized idea of the immortality of some or possibly most or all somatic cells has a bearing upon the problem of the origin of life on our planet. The experiments of Spallanzani, Schwann, Schroeder, Pasteur, Tyndall, and all those who have worked with pure cultures of micro-organisms, have proved that no spontaneous generation of living from non-living matter can be demonstrated; and the statements to the contrary were due to experimental errors inasmuch as the new organisms formed were the offspring of others which had entered into the culture medium by mistake.