THEORY OF LIFE 147 



Peculiarity of the organism. — Woodruff ob- 

 served the successive division of more than eight 

 thousand generations of unicellulars {Parame- 

 cium), without the death of a single organism. 

 Jacques Loeb said: "Unicellular organisms, like 

 bacteria, algae or infusorians, seem to be im- 

 mortal. They reach a certain size, divide into 

 two, each half growing again to full size and 

 dividing again, and so on. In this case we may- 

 say that it is practically the same individual 

 which continues to live in the successive genera- 

 tions. Small pieces of a cancerous tumor can be 

 transplanted successfully to other individuals 

 and these pieces grow again to a large size. This 

 process can also be repeated indefinitely, and it 

 is the same cancer cell which continues to live in 

 these successive transplantations, as it is the 

 same bacterium which continues to live in suc- 

 cessive generations. In this way it has been 

 shown that cancers in mice may outlive many 

 times the natural life of a mouse, in fact they 



seem to live indefinitely It seems that 



this is true also for certain normal cells like con- 

 nective tissue cells. Carrel has isolated connec- 

 tive tissue cells from the heart of a chick embryo 

 and cultures of these cells living on the extracts 

 from chick embryos have been kept alive now 



