CATALYSIS AND THE ENZYMES 



must consequently believe that the primary de- 

 composition of sugar in plant respiration is closely 

 related to alcoholic fermentation, if not identical 

 with it. This is another type of respiration pro- 

 cesses in the living cell. 



The aromatic substances on which oxidising 

 enzymes act seemed to have very little importance 

 for cell-life until Palladin, of St. Petersburg, whilst 

 working out experiments on plant respiration, 

 came to a remarkable hypothesis. Most of the 

 aromatic substances which are oxidised by the 

 enzymes furnish dark colouring matters as pro- 

 ducts of oxidation. This can be shown when killed 

 plants are kept in vapours of chloroform in an air- 

 tight glass vessel. Quite commonly they turn a 

 deep brown. Palladin supposes that such oxida- 

 tion processes take place even in living cells, but 

 the reduction of the colouring matters following 

 immediately, no staining becomes visible. The 

 aromatic substances therefore transfer the oxygen 

 of the air by means of oxidases to other oxidable 

 substances of the cell. This hypothesis explains 

 quite satisfactorily the existence of enzymes 

 which act only on aromatic substances, as well as 

 the position of the latter substances in the meta- 

 bolism of plants. 



No small number of lower organisms are able 



to live without a supply of air or free oxygen. 



Pasteur discovered this important fact in yeast 



and bacteria. Yeast may live as well without 



119 



