514 THE RESPIRATORY EXCHANGE 



temperature and the control of the nervous system over the 

 muscles, it is necessary to discuss the question in special reference 

 to man under natural conditions. Over all animals man is supreme 

 in his power of adapting himself to his surroundings or changing 

 his surroundings to suit his needs ; he can live either in the arctic 

 regions or in the tropics, for by means of appropriate clothing he can 

 readily control his loss of heat. Even unclothed a man can com- 

 pensate for considerable changes of external temperature, and this 

 he effects by altering both his loss and production of heat. Upon 

 the relative parts played by the physical and chemical methods of 

 regulation there has been much debate. Lowy concludes from the 

 results of fifty-five experiments upon sixteen men that the only 

 involuntary regulation of temperature in a man exposed to moderate 

 cold is effected by changes in the vascularity of the skin ; he found 

 that the respiratory exchange was unaltered in twenty experiments, 

 diminished in nine, and increased in twenty-six ; in the last series 

 the increase varied from 5 to 90'8 per cent, above the normal. 

 It is noteworthy that the greatest increase in the gaseous exchange 

 was observed in the men who shivered or moved, when they felt 

 cold, whereas no increase or even a decrease occurred in those 

 who remained ^quiet, and by an effort of the will suppressed any 

 inclination to move or shiver. This result has been confirmed 

 by Johansson. It must not be thought, however, that man is 

 an exception to the general rule that warm-blooded animals in 

 cold surroundings increase, in warm surroundings diminish, their 

 respiratory exchange and production of heat. The normal effect 

 of cold is increased muscular activity ; this is within the experi- 

 ence of every inhabitant of a temperate climate. The increased 

 muscular activity is not necessarily brought about by a conscious 

 effort of the will ; it is to a great extent produced reflexly. A 

 man works more energetically when the external temperature is 

 low, and, if he be obliged to remain inactive, the reflex effect of 

 cold may be so great as to produce shivering, forcible involuntary 

 movements which are accompanied by a great increase in the 

 respiratory exchange and production of heat. 



Observations upon both man and animals appear to show that 

 a very high external temperature will increase the respiratory 

 exchange ; the limits of regulation are apparently exceeded, the 

 tissues are abnormally heated and respond with increased respiratory 

 exchange. A condition in many respects similar is found in fever. 



