RESPIRATION AND FERMENTATION 275 



contains a small amount of iron, a special charcoal containing very- 

 little iron is used as a substitute; but by addition of traces of iron 

 the oxidizing power of such a charcoal is greatly increased. War- 

 burg's experiments on the effect of narcotics, such as ether, chloro- 

 form, etc., have been of great interest. These substances depress 

 considerably the rate of respiration in living cells. Their influence 

 on the charcoal model is the same. A complete parallelism has 

 been observed between the narcotic action and the capacity of 

 adsorption, which, in its turn, is proportional to the decrease of 

 surface tension. The only exception to this rule is shown by hydro- 

 cyanic acid, which even in very weak concentrations markedly 

 depresses respiration, though it is scarcely adsorbed at all. This 

 exception, however, is easily explained by the fact that HCN 

 unites readily with iron, forming a complex compound and thereby 

 removing it from the sphere of the oxidizing reaction. 



Warburg's conception of respiration, as a process occurring 

 on the surface of the colloidal particles of protoplasm rich in 

 iron, appears very attractive. It explains satisfactorily many 

 peculiarities of the respiratory process. The participation of 

 enzymes in respiration by no means is excluded, since they too 

 represent colloidal catalyzers having an enormous surface. Fur- 

 ther investigations may point to the best way of correlating the 

 absorption theory of Warburg with the enzyme theories of respira- 

 tion. It is to be hoped that in the next few years considerable 

 progress will be made in determining the internal chemistry and 

 mechanism of this fundamentally vital process. 



84. Influence of External and Internal Factors on Respiration 

 and Fermentation. — Representing as it does a very complex and 

 highly harmonious oxidation process, respiration is very little 

 dependent on external influences. It is regulated chiefly by 

 internal conditions. Of the latter, the most important is the pres- 

 ence of respiratory material, which, as has been seen, consists 

 chiefly of sugar. The rate of respiration is, therefore, rather 

 closely connected with the supply of carbohydrates. It decreases 

 considerably under conditions of starvation. This explains the 

 relation of respiration to exposure to light, established by Borodin 

 in one of his first experiments. When shoots with leaves are kept 

 in darkness, their respiration rate gradually decreases as the car- 

 bohydrates become exhausted. Upon exposure to light the supply 

 of carbohydrates is restored and respiration rapidly increases. 



