EFFECT OF MUSCULAR WORK AND TEMPERATURE. 



933 



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 dioxid elimination are 

 increased. This effect of temperature upon the body metabolism 

 is due mainly 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 to cause 

 shivering or muscular tension no increase in the excretion of CO 2 

 results. This fact suffices to explain, therefore, the physiological 

 value of shivering and muscular restlessness when the outside 

 temperature is low. The fact that variations in outside tempera- 

 ture affect only the consumption of non-protein material falls in, 

 therefore, with the conception of the nature of the metabolism 

 of muscle in activity, given above. When the means of regulating 

 * Johannson, "Skandinavisches Archiv f. Physiologic," 7, 123, 1897. 



