14 THE ACTION OF THE LIVING CELL 



albeit numerous theories of death have been borrowed 

 from physical sources, such as the spontaneous disinte- 

 gration of the radioactive elements. 



If one considers the energy changes accompanying 

 such transformations as a property of the radioactive 

 "life" of the element, then the "life" process ceases 

 when the substance has been completely transformed 

 to elements of lower atomic weights. Analogously, 

 some biologists have reasoned that the death of an 

 organism coincides with the exhaustion of some life- 

 giving substance. 



Other workers, notably Child, Loeb, and Pearl, 

 have adopted the alternative view that in the course 

 of life the organism suffers an accumulation of toxic 

 metabolites which finally attain a concentration suffi- 

 ciently great to interfere seriously with the normal 

 metabolic processes, so that death ensues. 



Nowadays it is generally accepted that the chemical 

 transformations upon which the organism depends 

 are determined by the presence of enzymes. In this 

 connection, it is worthy of note that in vitro experi- 

 ments with enzymes have frequently shown that the 

 latter are inactivated by the end-products of the 

 reactions which they catalyze. (Ter Muilen, 1905; 

 Morgulis and Beeber, 1928.) 



The careful investigations conducted by Woodruff 

 and his students have demonstrated unicellular organ- 

 isms to be immortal. The common ciliate, Para- 

 mecium, was found during a period of years to pass 

 through several thousand generations without the 

 intervention of natural death. Similarly, the in vitro 

 culture of the somatic cells of various higher animals 

 has indicated such cells to be potentially immortal. 



