400 



ANIMAL HEAT AND ITS REGULATION 



subject as the C0 2 curve. The discrepancies between the two are no more 

 than can be satisfactorily explained by this circumstance alone. 



If the C0 2 output at different hours of the day be obtained on the fasting 

 body in purposely enforced physical rest, it shows, as Magnus-Levy and espe- 

 cially Johansson have pointed out, but very slight variations ; and in the course 

 of any given period, the body temperature decreases because of the relatively 

 small metabolism. From which it follows that the above-mentioned varia- 

 tions in the intensity of metabolism are called forth primarily by the variations 

 in the movements and tension of the muscles occurring for one reason or 



another in the course of the 

 day. A cooperating factor, 

 though not of itself by any 

 means so potent as the mus- 

 cular work, is the increase of 

 metabolism due to taking 

 food. 



One inference from this 

 view is that with a reversal 

 of the daily habits, the tem- 

 perature variations ought to 

 be reversed. According to 

 some authors this actually 

 takes place. But Benedict 

 and Snell were unable to ob- 

 serve any perceptible tend- 

 ency to a reversal of the tem- 

 perature curve in the case of a man who, for ten successive days, worked at 

 night and slept by day, although the curve did vary decidedly from the normal. 



In my opinion one cannot conclude from these observations that other fac- 

 tors than those mentioned above are concerned in production of the daily varia- 

 tions of temperature. In this research the subject slept, as the authors remark, 

 a much shorter time than he was accustomed to, and it is in fact a fairly com- 

 mon experience that a man cannot accustom himself to a reversed mode of life 

 to the extent of completely converting day into night and night into day. On 

 this account the muscular activity cannot be exactly adjusted to the changed 

 order of life. Moreover, we possess observations on monkeys which show that 

 the reversed order does produce a complete reversal of the temperature varia- 

 tions. When these animals were kept for days either in complete darkness or 

 constantly in the light, the normal variations ceased and were replaced by quite 

 irregular ones (Galbraith and Simpson). 



Temporary changes of the body temperature in one direction or the other 

 may be produced by various voluntary acts which tend to increase either 

 the heat production or the heat loss. Thus the temperature falls as the result 

 of sitting perfectly still, of drinking cold water, etc. ; it rises as the result of 

 muscular work, etc. 



However, all these changes in the body temperature are as a rule very 

 insignificant, and this very remarkable fact has been established that the 



FIG. 148. The elimination of carbon dioxide in man, 

 determined every two hours. CO 2 , in 



grams. diurnal variation of temperature 



from the curve by Jiirgensen in Fig. 147. 



