510 



THE RESPIRATORY EXCHANGE 



The chick was placed in the respiration chamber with the water-bath 

 at 37'5, and ventilation was continued for thirty-five minutes before the 

 first period ; the young pigeon was in the ventilated chamber with the 

 water-bath at 38'5 for twenty-five minutes before the first period. 

 The periods are consecutive, and each determination of the output of 

 carbon dioxide is for fifteen minutes. 



The practical interest of the evolution of the warm-blooded 

 animal is centred in infants. Observations made by Babak upon 

 the respiratory exchange and the production .of heat in infants 

 have shown that the power of regulating temperature is imper- 

 fectly developed in the newly born. The regulation of the loss 

 of heat is imperfect, and its deficiency is clearly shown if the infant 

 be insufficiently clothed, when it is exposed even to moderate 

 cold ; the regulation of the production of heat by variations in 

 the combustion is also inadequate, and only within narrow limits 

 can the newly born child respond to changes of external tempera- 

 ture in a manner similar to that exhibited by the adult. Many 

 premature infants have been reared by proper attention to the 

 temperature of their surroundings ; the more premature and weak 

 the more nearly do they resemble cold-blooded animals in their 

 inability to regulate their temperature. The heat of their bodies 

 and their respiratory exchange vary with and in the same direction 

 as the external temperature. Cold, even moderate cold, to such 

 premature or weakly infants is not a stimulant but a depressant, 

 for they can regulate neither the loss nor the production of 

 heat. 



Thus it has been possible to trace the evolution of the warm- 



