THE VITAL UNITS CALLED CELLS I9I 



layers of the epidermis, skin cells, not muscle cells or sex 

 cells. But to explain all the differences existing between 

 fully developed cells on the basis of what is known of their 

 heredity is difficult because all of them, except the sex 

 cells, are known to inherit the same chromosome complex. 

 Here, as in the case of individuals, it is customary to fall 

 back upon the environment to which the cells must become 

 adapted if they are to survive. Young cells are more adaptable 

 than older ones and are immune to a lot of degenerative 

 changes by which the older ones are afflicted; they are also 

 better behaved; fewer of them become criminals. 



It is a kingdom rather than a democracy because the 

 nerve cells, though dependent for their position and all their 

 worldly goods upon the others, are born to this station, not 

 elected to it. They also control. The arrangement is in many 

 respects almost Utopian. 



The division of labor leaves nothing to be desired. There 

 is always an excess of willing hands (or cells) for every 

 basic industry, which we call the "physiological reserve." 

 This is exemplified by the observation that we can live 

 with one lung, one kidney or a third of our liver substance. 

 Yet normally there is no unemployment. The labor is 

 equally spread among the cells in each organ. To live, the 

 cells must work; otherwise like individuals they atrophy 

 from disuse and die as, for example, when labor is denied 

 them by the ruhng class of nerve cells. When the task 

 becomes harder they increase in size and power, again like 

 individuals. But this happy state of affairs does not last 

 forever. Inevitably the kingdoms rise and wane. Death 

 for the individual, made up of the kingdom of cells, is a 

 normal process. 



Internal disintegration may come in different ways 

 which we cannot discuss here. Reference may be made, 

 however, to the fact that the cells do not always attend to 

 their duties as they should do. When the kingdom has 

 attained the height of its efficiency and is on the downward 

 path (middle life and old age) some of the cells show an 

 alarming tendency to shake off the community control 

 which has been molded by nature during millions of years, 

 as laws have been formulated by the experience of the race. 



