42 GRAHAM LUSK 



7. Fasting animals show about the same ratio (R. Q.) as they do 

 when fed with meat, though usually a little less than under latter con- 

 ditions. During inanition fasting animals live off their own flesh, which 

 is of the same nature as the flesh which they eat. All fasting animals 

 present the picture of carnivora. 



8. The fact that the relation between the volumes of oxygon absorbed 

 and carbonic acid exhaled varies between 0.02 and 1.04 according to the 

 kind of food wliicfi the animal takes in, destroys the validity of the 

 hypothesis of l>riincr and Valentin (1840), attributing the respiration 

 to the simple diffusion of gases through membranes according to the laws 

 of Graham (which calls for a constant ratio of 0.85). In the text they 

 describe how they placed the bodies of animals (fowls, dogs, rabbits) in 

 an impermeable robber sack and found in mammals, as well as in birds, 

 that the total quantity of carbon dioxid eliminated from the skin and 

 intestine of these animals was practically negligible, rarely exceeding two 

 per cent of that found in the pulmonary respiration. 



9. Lavoisier tried to prove that the heat of the body came from the 

 oxidation of carbon and hydrogen. Rcgnault ami Reiset do not doubt 

 that the heat is in fact derived entirely from chemical reactions in the 

 body. But they think the reactions are too complex to be computed on the 

 basis of the oxygen intake. '"The substances which are oxidized are 

 composed of carbon, nitrogen, hydrogen, and often contain a considerable 

 amount of oxvgen. Though they be completely oxidized in the respiration 

 process, their own oxygen content contributes to the production of water 

 and carbonic acid, and the heat which is liberated is necessarily different 

 from that which would have been evolved by the oxidation of carbon and 

 hydrogen supposedly liberated. Moreover, the food substances are not 

 completely destroyed, for portions are converted into other materials 

 which play a special part in the body's economy and portions are trans- 

 formed into urea and uric acid. In all the transformation and assimilative 

 processes which these substances undergo in the organism there is either 

 liberation or absorption of heat ; but the processes are evidently so complex 

 that it is very unlikely that one will ever be able to calculate them." 



(They found in fowls that the volume of carbon dioxid was often 

 greater than the volume of oxygen, which rendered the proposition of 

 estimating the heat production from the oxygen impossible.) 



10. The quantity of oxygen varies during different periods of diges- 

 tion because of muscle work, and numerous other circumstances. In ani- 

 mals of the same species and the same weight the quantity of oxygen is 

 larger in young individuals than in adults. It is greater in healthy, thin 

 animals than in fat ones. 



11. The consumption of oxygen absorbed varies greatly in different 

 animals per unit of body weight. It is ten times greater in sparrows than 

 in chickens. Since the different species have the same body temperature 



