936 



NUTRITION AND HEAT REGULATION. 



given off. Pettenkofer and Voit found that the carbon dioxid 

 eliminated by a man during a day of work was nearly double that 

 excreted during a day of rest. Along with this rise in the carbon 

 dioxid excretion there is a corresponding increase in the absorption 

 of oxygen. These results are well illustrated in the following 

 table, which shows the effect of posture and of severe muscular 

 work upon the hourly excretion of carbon dioxid and absorption of 

 oxygen (Benedict and Carpenter).* 



Metabolism During Sleep.^ — It has been shown that during 

 sleep there is no marked change in the total nitrogen excreted, 

 and therefore no distinct decrease in the protein metabolism. 

 According to Siven, there is a distinct diminution in the secretion 

 of the endogenous purin nitrogen. On the contrary, the carbon 

 dioxid eliminated and the oxygen absorbed are unquestionably 

 diminished. This latter fact finds its simplest explanation in the 

 supposition that the muscles are less active during sleep. The 

 muscles do less work in the way of contractions, and, in addition, 

 probably suffer a diminution in tonicity, which also affects their 

 total metabolism. 



Effect of Variations in Temperature. — In warm-blooded 

 animals variations of outside temperature within ordinary limits 

 do not affect the body temperature. An account of the means by 

 which this regulation is effected will be found in the chapter upon 

 Animal Heat. So long as the temperature of the body remains con- 

 stant, it has been found that a fall of outside temperature may 

 increase the oxidation of non-protein material in the body, the in- 

 crease being in a general way proportional to the fall in tempera- 

 ture. That the increased oxidation affects the non-protein con- 

 stituents is shown by the fact that the nitrogenous excreta remain 

 unchanged in quantity, other conditions being the same, while 

 the oxygen consumption and the carbon choxid elimination are 

 increased. This effect of temperature upon the body metaboHsra 

 is usually explained as being due to a reflex stimulation of the motor 

 nerves to the muscles. The temperature nerves of the skin are 

 affected by a fall in outside temperature, and bring about reflexly 

 an increased innervation of the muscles of the body. Indeed, it 

 is stated* that unless the lowering of the temperature is sufficient 



* Carnegie Institution of Washington, No. 126, 1910. 



t Johannson, "Skandinavisches Arcliiv f. Physiologic," 7, 123, 1897. 



