RESPIRATION 25 



determined to experiment. In the plant, on the contrary, . 

 other substances than dextrose may become oxidized, or the 

 oxidation of dextrose may be incomplete. In the laboratory 

 one can deal with definite quantities of isolated substances ; 

 in the living organism indefinitely known quantities of 

 many substances together are acted upon. Animal physi- 

 ologists have done much more in this direction than have 

 plant physiologists, and the high organisms which they 

 study are better suited for the purpose than are plants. 

 The relatively high body-temperatures of warm-blooded ani- 

 mals permit direct temperature determinations from weighed 

 quantities of known foods eaten, as well as calculations 

 from the amounts of oxygen needed to effect combustions 

 or decompositions. Thus the animal physiologist can check 

 the results obtained by one method with those obtained by 

 other methods. The results of animal physiologists indicate 

 that only about 95% of the calculated yield of energy from 

 oxidation* appears as heat. So then we must regard these 

 figures as somewhat too high, but their suggestive value is 

 great whatever must be admitted as to their exact numeri- 

 cal value. 



The larger organisms demand for the normal execution of 

 their functions more energy than can be supplied by the re- 

 arrangement of the component atoms of already furnished 

 molecules ; they must oxidize these molecules, and the more 

 complete the oxidation, the greater the amount of energy 

 liberated. Some of the smaller organisms supply them- 

 selves with adequate amounts of energy by the destruction 

 of complex compounds within their own living cells. Proba- 

 bly some of the cells of all organisms have recourse, at 

 times at least, to the same means of securing needed energy, 

 and when free oxygen is not obtainable the majority of 

 organisms can continue living for a time by so doing. 

 From this the general inference may safely be drawn, that 

 the ability to obtain needed energy by the destruction of 

 complex substances in the cells is inherent in all organisms ; 

 that in the majority of organisms and of their component 



* See Pembry in Schafer's Physiology, vol. I., pp. 836-7. 



