THE VARIATIONS DURING LIFE 



121 



(Lehmann, Miiller, Munk, Senator and Zuntz [1893]), that the standard 

 gas exchange per kg. remains constant even during a prolonged fast. 1 

 This result has on the whole been confirmed by Benedict's recent in- 

 vestigation [1915] of a prolonged fast in man. It has been extended 

 also to other mammals and can probably safely be accepted as ap- 

 proximately valid for all warm-blooded animals, but whether it can be 

 extended to cold-blooded also is uncertain and unlikely. 



A. V. Hill [1911] found in calorimetric experiments on frogs kept in 

 darkness in a Dewar flask conditions in which they usually remain very 

 quiet, so that the metabolism probably approaches the standard that 

 the production of heat fell off during the first two weeks of inanition 

 from 0-55 cal. per c.c. of frog per hour to O'26 cal., but afterwards re- 

 mained remarkably constant as shown by fig. 35. This indicates, ac- 



50 



35 



FIG. 35. From "Journal of Physiology" (Cambridge University Press). 



cording to Hill, that the amount of reserve material stored in the tissues 

 determines to a certain degree the intensity of the metabolic processes. 

 The experiments are not sufficient, however, to prove this contention, 

 because it is possible that a decrease in muscular tone may be primar- 

 ily responsible for the decrease in metabolism, but it appears to be 

 supported by casual observations made by the writer and others, and a 

 comprehensive investigation of this problem, in which standard condi- 

 tions were rigorously maintained and both oxygen, carbon dioxide 



1 In a recent investigation Zuntz [1913] found on a dog which was for a long time 

 given an insufficient amount of food that the metabolism calculated per square metre 

 decreased considerably during 10 months from 931 cal. in 24 hours, when the dog weighed 

 10 kg., to 631 when the weight had gone down to 4-98 kg. Then it rose again, however, and 

 reached 921 cal. (weight 4*1 kg.) before the animal died. 



A similar experiment was made simultaneously by Morgulis [1913] who obtained a 

 rather different result. 



