VITAL RESERVES 321 



tive index of the relative metabolism of these parts. 

 Craigie (1920, 1921, 1925), in a series of observations 

 on the vascularity of the brain of the rat, brings to 

 light some very interesting facts. 



The primary sensory centers, like those illustrated 

 in Figure i (p. 39), are more richly vascularized than 

 are the motor centers. This is correlated with the fact 

 that in the sensory centers there is a considerable 

 amount of correlation, a physiologically expensive 

 "legislative" function, while the motor centers are 

 concerned with the physiologically simple "adminis- 

 trative" processes (Herrick, 1924, pp. 245, 257). 



In the cerebral cortex of the rat Craigie has in- 

 vestigated the relative vascularity of five regions — 

 parietal, occipital, temporal, precentral, insular — 

 whose vascular richness diminishes in the order given. 

 The charts accompanying his paper (1921, Fig. i) 

 show that the somesthetic-motor region has the rich- 

 est blood supply and the insular cortex the poorest. 

 The areas examined in the occipital and temporal 

 regions lie at the margins of the visual and auditory 

 fields, respectively. In view of the theory of the or- 

 ganization of the associational cortex of the rat al- 

 ready presented (p. 251 and Fig. 51), it would be in- 

 teresting to learn how the vascularity of these two 

 marginal areas compares with that of the central 

 points of the visual and auditory projection fields. 



In the developing cortex, capillary richness is di- 

 rectly related with the rise of functional activity, and 



