RESPIRATION 685 



cycle possibly increasing with oxygen tension. Whatever the explanation, 

 these are excellent examples of how inhibition can vary with the experi- 

 mental conditions and why the results of different investigators do not 

 always check. The effects of glucose concentration on the inhibition of yeast 

 respiration by 1 mM arsenite have bearing on this general problem (see 

 accompanying tabulation) (Dresel, 1928). Here too there is at least a 



superficial correlation between the inhibition and the respiratory rate. 

 Administration of thyroid increases the respiratory rates of tissues and 

 increases the susceptibility of animals to arsenite (Hildebrandt and Nishi- 

 ura, 1924) and organic arsenicals (Dybing, 1948). However, no significant 

 differences were found in the effects of arsenite on the respiration of normal 

 and hyperthyroid rat brain (Cohen and Gerard, 1937). The entire problem 

 of the effects of metabolic rate on inhibition needs further investigation, 

 since it is an important consideration in attempting to explain the differ- 

 ential effects of inhibitors on different tissues and tissues operating at 

 various functional levels. 



The respiration of liver slices from thiamine-deficient rats is inhibited 

 by arsenite more strongly than that of normal liver (see accompanying 

 tabulation) (Goldschmidt and Lewin, 1937). Addition of thiamine to 



Liver , ,^, Respiration % Inhibition 



(miH) 



Normal — 4 . 85 



Normal 10 4.01 17 



Deficient — 3.07 



Deficient 10 2.02 34 



the slices (a) increased the respiration and the inhibition of normal liver, 

 and (b) decreased the respiration and abolished the inhibition of deficient 

 liver, results which are so odd that confirmation is required. One is tempted 

 to relate the greater sensitivity of avitaminotic liver to the lack of thiamine- 

 PP and consequent impairment of keto acid oxidation, but inasmuch as 

 cyanide also inhibited the deficient tissue more strongly it might be better 



