JANSKY 



not performing at maximal capacity when the animal is engaged in 

 maximal steady state effort. This may explain the tendency for cyto- 

 chrome oxidase values to be higher than maximal working metabol- 

 ism in the various species. 



It is, therefore, suggested that the terms "maximal steady state 

 metabolism," be used for values obtained in vivo and "total cyto- 

 chrome oxidase activity" be used for values obtained in vitro, which 

 represents the highest theoretical value of oxidative metabolism 

 (metabolic capacity). 



Cytochrome Oxidase Activity in Body Organs 



The values of total cytochrome oxidase activity are useful for 

 comparative purposes and seem to be especially suitable for esti- 

 mating the metabolic capacity of different body organs. At present, 

 we do not know of any other method for assessing maximal perform- 

 ance of body organs. The cytochrome oxidase method can provide 

 some information on the relative roles of different organs in the total 

 metabolic capacity of the whole animal. 



The cytochrome oxidase activity was measured in 10 of the most 

 important organs (carcass, liver, skin, kidney, brain, lung, heart, 

 diaphragm, spleen, and gonads) in the golden hamster (Svoboda and 

 Jansky, 1959). Some other preliminary experiments were made on 

 the white mouse and on the rat. 



In general, the highest cytochrome oxidase activity per mg of 

 dry substance was found in the heart, kidney and brain, the lowest in 

 the carcass and in the skin. The cytochrome oxidase activity per mg 

 dry substance in the same organs of various species seems to de- 

 crease in heavier animals. 



The most important consideration for our purposes is the ratio 

 of cytochrome oxidase activity in whole organs to the total cyto- 

 chrome oxidase activity ofthe whole animal. The results on the gold- 

 en hamster show veryclearly that the muscles play the most impor- 

 tant role. At body temperature (37 G), they rep resent about 76% of 



186 



