Respiration and Metabolism 



227 



such forms as coelenterates with a high water content and the more soHd forms, 

 and further that the phylogenetically advanced groups show a higher rate of 

 metabolism than the more primitive ones (Fig. 47). 



The higher "reaction rate" of smaller animals is associated with increased 



TABLE 38. OXYGEN CONSUMPTION OF SMALL ADULT MAMMALS 

 UNDER APPROXIMATELY BASAL CONDITIONS 



need of oxygen, but the matter of heat loss is also important in the metabolic 

 economy of small animals, particularly in that of homoiotherms with inade- 

 quate insulation. Mice huddled together apparently for warmth consume less 

 oxygen as a group than they do when separated and measured individually.-^^ 

 However, in the absence of data on body temperature and activity, absolute 

 values are not available for a close comparison of these groups. Similar evidence 

 on the brown snake, a poikilotherm, shows this aggregation-oxygen decrease 

 effect."^" 



Oxygen consumption studies by Scholander (personal communication) on 

 arctic, temperate, and tropical mammals indicate that the metabolic regulation 

 may be in part a function of the insulation efficiency of the body surface and 

 in this respect correlated with surface area. Heat production along with oxygen 

 consumption tends to follow roughly the surface rule, the weight raised to the 

 0.66 or 0.73 power. A linear relationship is obtained when the log of the heat 

 production is plotted against the log of weight (Fig. 48).^'^ 



A correlation between oxygen consumption and brain weight was made by 

 Crile,'^'* for a number of invertebrates and vertebrates from various phyla. The 

 correlation apparently reflects the relation of body surface area to brain weight, 

 but represents more significantly the dependence of metabolism on the dis- 

 tribution of active protoplasm. 



