456 EDWARD HORNE CRAIGIE 



great as that of the ventral cornu of the spinal cord or that of 

 the hypoglossal nucleus? While there is no proof that such a 

 difference in vascularity necessarily implies a corresponding 

 difference in metabolic activity in the regions concerned, that 

 assumption, as made by Aby, seems to be the only reasonable 

 explanation (in so far as it is an explanation) of the facts. More- 

 over, it is quite in accord with what is known of the blood supply 

 to other tissues (e.g., Krogh, '19). The considerable individual 

 variations observed suggest that the correspondence is not very 

 exact, and no doubt each region is supplied somewhat in excess 

 of its normal requirements. It is difficult to believe, however, 

 that there would be any constant and considerable differences, 

 such as have been demonstrated, if the quantity of materials 

 used and of waste products given off were about the same in 

 the various parts compared. Also, the metabolic differences 

 must really be considerable and regular, as the vascularity sug- 

 gests, for any small or occasional variations in chemical activity 

 could probably be satisfactorily dealt with by the cerebrospinal 

 fluid (Halliburton, '16; Weed, '17) and, perhaps, the neuroglia, 

 as suggested above. The observation of Hatai ('17), that "the 

 relation between metabolic products and active cell substance 

 is quantitatively similar in all parts of the central nervous system 

 and in both parts of the neurone," seems to indicate that much 

 more of these substances must be produced in certain parts, as 

 otherwise the much greater blood supply in these parts would 

 cause them to be much poorer in residual products of metabolism, 

 which are what Hatai measured. His conclusion, that the quanti- 

 tative relation which he demonstrates between the active cell 

 substance and the metabolites indicates "an equality in activity 

 so far as nitrogen metabolism is concerned," does not appear 

 to agree with the facts regarding the blood supply which are 

 recorded above. 



If the metabolic processes are not much more active in the 

 richly vascular regions than in the poor ones, we might expect 

 that the cells in the latter would probably be the first to succumb 

 to anaemia. This, however, is by no means the case. The 

 small pyramidal cells in the cortex survive only eight minutes, 



