84 



THE ORGANIZED ANIMAL 



you see before you would not be there. 

 Death put in its appearance when or^raniza- 

 tion of cells occurred, that is, when some 

 of the individual cells lost the power to 

 reproduce, and hence were sacrificed in 

 order that those that were able to repro- 

 duce could continue. This seems to have 

 been the penalty for organization and spe- 

 cialization. 



It is difficult to understand why cells that 

 are separate, free from other cells, may con- 

 tinue living forever, whereas others that are 

 bound together into a mass eventually die 

 even though apparently all of their basic 

 needs are satisfied. Perhaps during the 

 process of evolution the organization was 

 not quite perfect, that is, the individual 

 cells were not completely cared for, or 

 perhaps the whole organization slowed 

 down after a certain period of time and 

 could not keep pace with the demands of 

 all the cells. This point has long intrigued 

 biologists and has resulted in some very 

 fruitful research. 



If it were possible to grow tissues away 

 from the animal of which they are a part, it 

 would be possible to determine whether or 

 not such cells once released from their in- 

 tended environment could survive like 



single isolated cells. This was first done in 

 1907 by Ross G. Harrison, who grew em- 

 bryonic tissues in flasks by feeding them 

 special nutrients. Alexis Carrel, employing 

 similar methods, kept embryonic chick 

 heart tissues alive for over 30 years. At the 

 end of this period of time, about three times 

 the normal life span of a chicken heart that 

 remained with its owner, the cells were ac- 

 tive and appeared not to have changed at 

 all. They apparently have the capacity to 

 live forever, just as single-celled animals 

 do. In other words, metazoan cells still 

 retain their power of immortality. It is only 

 when they become incorporated into a 

 community of cells in the body that they 

 undergo the changes which we associate 

 with senescence. Something is not quite 

 right in the animal body and causes a cell 

 to fail. The delicate adjustment of youth 

 and maturity is thrown out of tune so that 

 eventually some cells do their job so poorly 

 that the complete organism cannot main- 

 tain life. It is not at all impossible that some 

 day the exact reason for this lack of adjust- 

 ment will be discovered and metazoan cells 

 will regain their immortality. Imagine the 

 social upheaval such a discovery would 



cause! 



