228 



Comparative Animal Physiology 



In conclusion, although many correlations have been demonstrated between 

 metabolic rate and functions of the body weight approximating surface area, 

 there is scant evidence to indicate the causes for this relationship. The cor- 

 relation reflects the changing activity of the protoplasm of the body cells. 

 Whether this condition will be demonstrated as due to decrease in rates of 

 chemical reactions, enzyme concentrations, growth substances, or whatever, 

 must depend on future investigations. 



Oxygen Consumption in Relation to Age. No simple correlation can be 

 made between oxygen uptake and age; rather, the different phases of develop- 



30.000 - 



« 10.000 - 



uj 1.000 



.100 



.010- 



.003 



I 10 100 



BODY WEIGHT - gmi. 



1000 



Fig. 46. Double log plots of oxygen consumption and body weight of the kelp crab, 

 Pugettia, and of several related Crustacea. From Weymouth et al.^^ 



ment must be considered separately. Oxygen consumption of young animals 

 is higher than that of their older relatives, indicating in some measure the size 

 relationship considered above (Fig. 49). Older organisms tend to "run down" 

 as oxygen-consuming processes go on less rapidly, a phenomenon possibly 

 associated with total enzyme concentrations of the young and older organisms. 

 A peak in metabolic activity is usually well marked a short while after birth 

 or hatching, as, for example, in the chicken (Fig. 50). The period of greatest 



