DEATH AND THE DURATION OF LIFE 91 



three score and ten to about 27 times that length, i.e., to 

 about nineteen hundred years. Unfortunately our body 

 does not tolerate any considerable lowering of its tem- 

 perature and if it did, life at so low a temperature would 

 probably become very monotonous and uninteresting since 

 in all probability sensations of pleasure as well as pain, 

 of joy and of sadness, would be at a very low level. 



The experiments on aseptic flies therefore lend support 

 to the idea that the duration of our life is the time re- 

 quired for the completion of a chemical reaction or a 

 series of chemical reactions. If these reactions consist 

 in the gradual accumulation of harmful products in our 

 body, or in the gradual destruction of substances required 

 for a youthful condition, we understand why senile decay 

 and death are the natural result of life. 



Ill 



Unicellular organisms, like bacteria, algae or infusorians, 

 seem to be immortal. They reach a certain size, divide 

 into two, each half growing again to full size and divid- 

 ing again, and so on. In this case we may say that it is 

 practically the same individual which continues to live in 

 the successive generations. Small pieces of a cancerous 

 tumor can be transplanted successfully to other individ- 

 uals 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 succes- 

 sive transplantations, as it is the same bacterium which 

 continues to live in successive 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. Cancer cells may therefore be called 

 immortal as was pointed out by Leo Loeb many years 

 ago. 



It seems that this is true also for certain normal cells 

 like connective tissue cells. Carrel has isolated connec- 

 tive tissue cells from the heart of a chick embryo and 



