70 PHYSIOLOGY, CHAP. 



system, which regulates both the production and the loss of 

 heat. 



Sonde'n and Tigerstedt (1895) determined from hour to hour 

 the quantity of carbon dioxide discharged, and found that the 

 curve of the daily variation in temperature corresponded very 

 closely with that of the discharge of carbon dioxide. They came 

 to the conclusion that the variation in temperature coincides with 

 a variation in the intensity of the exchange of material. 



Without detracting from the value of this conclusion, it does 

 not seem to me to contradict the theory that the nervous system, 

 by controlling the chemical phenomena of the organism, acts as 

 the regulator of tliermogenesis. It merely leads us to the conclusion 

 that the hypothermia of the night and the hyperthermia of the 

 day are due respectively to diminished and increased production 

 of heat, and not to increased and diminished loss. 



Tigerstedt, however, considers the most important cause of the 

 daily variations in temperature to be the muscular movements 

 which take place while the body is in a state of rest in bed. His 

 pupil, Johanssohn (1897), noticed that when sitting still or lying 

 in bed in a fasting condition we intentionally avoid making any 

 movement, the discharge of carbon dioxide during the different 

 hours of the day varies very little as compared with the variations 

 noticed in ordinary conditions of nourishment and relative rest. 

 Even in these conditions, however, there is the characteristic daily 

 variation in temperature ; the minimum is noticed at 4 A.M., and 

 the maximum at 7 P.M., although the difference between the two 

 only amounts to 0'5, as against 1'1 under ordinary conditions. 

 This proves to my mind that while muscular activity is an 

 important factor in regard to the combustion and temperature of 

 the body, it does not afford an adequate explanation of the daily 

 variations of temperature. Everything tends to prove that this 

 variation is an outward expression of an alternation of activity and 

 rest in the nervous system, a view which would agree with the 

 old theory advanced by Chossat, who considered the nightly fall 

 in temperature to be due to rest and sleep, to the cessation of all 

 the stimuli which act on the nervous system during the hours of 

 wakefulness, and tend to increase the metabolism and the tempera- 

 ture. He found, indeed, that if animals are awakened during the 

 night, their temperature rises, and soon reaches the point which he 

 observed normally in the morning. 



Is it possible to invert the daily variation in temperature by 

 inverting the usual mode of life, that is, by sleeping during the 

 day and remaining awake, eating, and working during the night ? 

 Krieger (1869) appears to have been the first to try this experi- 

 ment. He states that he succeeded in obtaining a complete 

 inversion of the daily curve of temperature; he i did not, however, 

 give the exact data of his observations. Debzynski (1875), by 



