METABOLISM 63 



with free oxygen if it is present or with 

 any of the substances in the organism 

 with which it can combine. If the cell 

 has been stained with methylene blue 

 the hydrogen unites with it forming a 

 colorless compound. This has been pro- 

 posed as a test of life. It is, however, 

 not certain that it occurs in all living 

 cells and it can easily be imitated by non- 

 living materials. 



There are certain organisms which do 

 not carry the process of respiration to the 

 point of producing carbon dioxide and 

 which therefore differ from the majority 

 of animals and plants. 



Plants and animals which require free 

 oxygen quickly show the effects of a de- 

 ficiency in the oxygen supply. They be- 

 have as if anesthetized; but if not kept 

 too long in this condition they recover 

 completely when the normal supply of 

 oxygen is restored. This led Verworn to 

 think that anesthetics produce their ef- 

 fects by depriving the cells of their nor- 

 mal supply of oxygen because they di- 



