494 



THE RESPIRATORY EXCHANGE 



curves (Fig. 26). Thus it is that a small animal has a far greater 

 surface in relation to its weight than has a large animal. The 

 smaller mammals and birds have an internal temperature which 

 is as high or even higher than that of the bigger animals ; it there- 

 fore follows that owing to its relatively greater cutaneous surface 



FIG. 26. Weight and Surface of Body at Different Ages. 

 Proteid required ( Waller.) 



WW= body-weight in kilos (1 mm. = 1 kilo). 

 SS = body-surf ace in sq. metres (1 cm.=l sq. metre). 

 SS = body-surf ace per 1 kilo body-weight in sq. cms. (1 cm. =1 grm.). 

 NN = proteid per kilo body-weight in grms. (1 cm. =1 grm.). 



the small animal must possess either a special covering of fur or 

 feathers for the prevention of an excessive loss of heat or a more 

 rapid production of heat than the big animal. Both means are 

 employed, but here it is only necessary to discuss the latter. An 

 increased production of heat necessitates increased combustion, 

 increased absorption of oxgyen and discharge of carbon dioxide, 



