THE FASTING KATABOLISM 261 



tion from the older one and the fat from the thin one and the 

 beef steer and dairy cow, e.g., are far from being geometrically 

 similar. Additional determinations of the relation of surface 

 to weight in different species, types and ages of domestic ani- 

 mals would be of much interest but in their absence the method 

 of comparison just outlined may probably be assumed to give 

 a fair approximation to the truth and is certainly more accurate 

 than a simple computation in proportion to weight. 



348. Muscular activity. As was implied in the introductory 

 section of Chapter VI (274), and as will appear in greater detail 

 in Chapter XIV, muscular work is done at the expense of energy 

 derived from the katabolism of body substance, and no other 

 single factor so largely influences the total katabolism. The 

 minimum fasting katabolism which represents the demands of 

 the indispensable life processes is exhibited only ifl a state of 

 complete muscular rest. It is rarely the case, however, that an 

 animal, even when at rest in the ordinary sense, does not main- 

 tain more or less muscular tension or execute more or less mo- 

 tions of various parts of the body, all of which, even when 

 apparently slight, involve in the aggregate considerable ex- 

 penditure of energy. 



Zuntz and Hagemann, 1 for example, report a respiration experiment 

 upon a horse in which the uneasiness caused by the presence of a few 

 flies in the chamber of the apparatus caused an increase of 10 per 

 cent in the metabolism. Johansson 2 found the hourly excretion of 

 carbon dioxid by a fasting man when simply lying in bed (awake) 

 to be 24.94 grams as compared with 20.72 grams when all the muscles 

 were as perfectly relaxed as possible. Benedict and Carpenter 3 have 

 compared the metabolism of men during sleep with that of the same 

 subjects lying quietly in bed immediately after waking. In the three 

 cases which they regard as strictly comparable the increase in the 

 heat production during the waking period ranged from 5.8 to 15.2 

 per cent, averaging 11.4 per cent. Benedict and Talbot, 4 in experiments 

 upon infants, found that even scarcely noticeable muscular activity 

 produced a most marked effect on the carbon dioxid excretion, and 

 Benedict and Pratt 5 have noted similar results with dogs. 



. Jahrb., 23 (1894), 161. 



2 Skand. Arch. Physiol., 8 (1898), 85. 



3 Carnegie Institution of Washington, Publication No. 126 (1910), p. 241. 



4 Amer. Jour. Diseases of Children, 4 (1912), 129. 

 6 Jour. Biol. Chem., 15 (1913), i. 



