260 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



is reached. Below this temperature shivering is largely abolished by the 

 cold itself and oxygen consumption falls as described above (see fig. 1 ) . 



This diminished oxygen consumption is paralleled by a decreased car- 

 bon dioxide production, but our measurements were not sufficiently exact 

 and well controlled to enable one to say definitely whether the metabolic 

 respiratory quotient changes or remains constant as the temperature is 

 lowered. 



Such measurements would be of interest because they might give a 

 clue as to whether cooling alters the metabolism qualitatively as well as 

 quantitatively. 



1200 ,00 ^,^^ 



Fig. 1. Effect of cooling on pulmonary ventilation and gas exchange in 

 anesthetized dog. 



a lightly 



VENTILATION 



The partial pressures of carbon dioxide and oxygen in the alveolar gas 

 are determined by the ratios of alveolar ventilation to carbon dioxide 

 elimination and to oxygen uptake respectively. During cooling, therefore, 

 the partial pressures of these gases will remain unaltered if ventilation 

 diminishes proportionately at the same rate as does metabolism. In the 

 anesthetized dog, however, ventilation decreases during cooling relatively 

 more than does metabolism, with hypoxia and respiratory acidosis as con- 

 sequences. At a body temperature of between 20° and 25°C breathing 

 ceases entirely and death occurs if artificial ventilation is not instituted 

 (see fig. 1). This cessation of breathing is jirobably the manifestation of 

 a functional failure somewhere in the neural mechanism controlling breath- 



