56 Can Science Explain Life? 



upon by external forces, and it has never been 

 shown that physical disturbance is necessary for 

 cell division when the necessary food materials 

 and environmental conditions are present. 



Cell division cannot be attributed to surface 

 tension because the effect of surface tension is 

 always to hold a body together and never to sepa- 

 rate it into fragments, but even if surface tension 

 would act in the opposite direction from that in 

 which it actually does act it would still be insuffi- 

 cient to account for cell division because the co- 

 hesive strength of protoplasmic fibers is far 

 greater than any force that could possibly result 

 from surface tension. For example, a single 

 human hair will sustain a tension of about 40,000 

 dynes, whereas a filament of physiological salt 

 solution of the same dimensions will sustain a ten- 

 sion of only about one dyne. 



Another suggestion has been that cell division 

 might be due to the fact that as an organism be- 

 comes larger its food requirements increase with 

 the third power of its linear dimensions whereas 

 the quantity of food within reach increases only 

 as the first or second power. This explanation is 

 also inadequate because shortage of food would 

 only cause an organism to become under-nour- 

 ished, which might retard its growth and even- 

 tually result in its death, but would not cause it to 



