LIVING SUBSTANCE 133 



it may be said that such organisms exist in the condition of 

 " Scheintod " (apparent death). 



2. Life and Death 



It has been seen that the determination of the difference between 

 life and apparent death is beset with practical difficulties, since it 

 is not easy to decide experimentally whether the life-process in 

 reality is at a complete standstill in dried and apparently dead 

 organisms. It is still more difficult to determine theoretically a 

 sharp limit between life and death. 



In daily life it is easy to distinguish the dead organism from the 

 living ; for from the human body and from the higher animals we 

 have formed a general conception of death, and are accustomed to 

 consider it as occurring at the moment when the heart, hitherto 

 never quiet, stands still, and the individual ceases to breathe. 

 But we here follow the superficial habit of daily life and take into 

 consideration only the gross differences that make their appearance 

 at that time, without noticing the continuance of certain phe- 

 nomena after this all-important moment. 



The criterion of life is formed only by the vital phenomena, i.e., 

 by the various phases in which the vital process, or the metabolism, 

 becomes evident to the senses. But if this criterion be applied to 

 the human being at the moment usually termed the moment of 

 death, it is found that in reality he is not then dead. A careful 

 examination shows at once the truth of this statement. 



It is true that the spontaneous gross muscular movements cease, 

 the man becomes relaxed and quiet. But the muscles frequently 

 remain for several hours sensitive to external influences, responding 

 to the latter with twitchings and movements of the limbs, in other 

 words showing vital phenomena. A moment even comes when the 

 muscles gradually contract once more spontaneously, this is the 

 death -stiffening (rigor mortis). Not until this has passed is the 

 life of the muscles extinguished. Nevertheless, even then the body 

 is not entirely dead. Certain parts only, certain organs or cell- 

 complexes, such as the cells of the nervous system and of the 

 muscles, no longer show vital phenomena ; but other cells and cell- 

 complexes continue to live unchanged long after rigor mortis has 

 passed. As is well known, the inner surface of the air-passages, the 

 larynx, the trachea, and the bronchial tubes, is covered with a ciliated 

 epithelium, a layer of cylindrical cells pressed tightly together and 

 bearing upon their surface fine hair-like appendages, with which 

 they perform a continual, rhythmic, beating motion (Of. Fig. 20 a, 

 p. 78). These ciliated cells continue their normal activity in the 

 corpse for days after the cessation of the heart, and thus survive 

 after the so-called death. But even after several days the whole 

 body is not always dead. The white blood-corpuscles, or leucocytes, 

 the amoeboid cells that are not only carried about passively in the 



