DEATH 



individuals. In many of the algae and liverworts (even 

 in the bryophyllum, closely related to the stone-crop, or 

 sedum) — as well as in the common fresh-water polyp, 

 hydra, and other polyps — every bit that is cut off is 

 capable of growing into a complete individual. But the 

 higher the organization is developed and the closer the 

 correlation of the parts and their co-operation in the life 

 of the centralized stock or person, the slighter we find 

 the regenerative faculty of the several organs. Even 

 ' then, however, many used-up cells may be removed and 

 replaced by regenerated new cells. In our own human 

 organism, as in that of the higher animals, thousands of 

 cells die every day, and are replaced by new cells of the 

 same kind, as, for instance, epidermic cells at the surface 

 of the skin, the cells of the salivary glands or the mucous 

 lining of the stomach, the blood-cells, and so on. On 

 the other hand, there are tissues that have little or noth- 

 ing of this repairing power, such as many of the nerve- 

 cells, sense-cells, muscle-cells, etc. In these cases a num- 

 ber of constant cell-individuals remain with their nucleus 

 throughout life, although a used-up portion of their cell- 

 body may be replaced by regeneration from the cyto- 

 plasm. Thus our human body, like that of all the 

 higher animals and plants, is a "cell -state" in another 

 sense. Every day, nay, every hour, thousands of its 

 citizens, the tissue-cells, pass away, and are replaced 

 by others that have arisen by cleavage of similar cells. 

 Nevertheless, this uninterrupted change of our personal- 

 ity is never complete or general. There is always a 

 solid groundwork of conservative cells, the descendants 

 of which secure the further regeneration. 



Most organisms meet their death through external or 

 accidental causes — lack of sufficient food, isolation from 

 their necessary environment, parasites and other enemies, 

 accidents and disease. The few individuals who escape 

 these accidental causes of death find the end of life in 



105 



