VASCULARITY IN THE NERVOUS SYSTEM 451 



Hill and Nabarro ('95) found the oxygen consumption and the 

 carbon-dioxide production in the brain to be low, while Alexander 

 and Cserna ('13) found it to be very high — so high as to cast 

 doubt upon their results (Bayliss, '18). The dark color of the 

 blood in the cerebral veins, as Bayliss points out, suggests that 

 there has been a very considerable consumption of oxygen, and 

 Tashiro's experiments ('17 and earlier papers) lead him to believe 

 that there is a rather high production of carbon dioxide in nerves 

 and ganglia. Mac Arthur and Jones ('17), studying ground 

 tissue, reached a similar conclusion regarding the central nervous 

 system. There are also two recent papers by Moore ('18, '19) 

 reporting a high acid production rate in the medulla, but a low 

 one in the sciatic nerve. It may be noted in this connection 

 that the total flow of blood through the brain in a given time 

 is much greater than that through skeletal muscle and most 

 other parts of the body (Jensen, '04). The most generally 

 accepted view, however, appears to be that respiratory activity 

 in nervous tissue is low. 



Again, A. V. Hill's investigations ('12) are claimed to prove 

 that the evolution of heat in nerve fibers is so small that any 

 metabolism is doubtful, while recently Baglioni ('17) has shown 

 that there is a distinct, though not high, production of heat in 

 the central nervous system of the toad, which, moreover, bears 

 a definite relation to functional activity. 



Whether metabolic activity is high or low, there is still the 

 question of what relation it bears to functional activity. "The 

 problem of the essential physico-chemical nature of nerve con- 

 duction .... is still regarded by most physiologists as 

 unsolved, and apparently by many as insoluble" (Lillie, '18). 

 Probably the most generally accepted opinion regarding the 

 nervous impulse is that summed up by Bayliss as follows : 



That it is a reversible, physico-chemical process, not associated with 

 loss of material on account of metabolic reactions, is indicated by the 

 following facts : 



Incapability of fatigue under normal conditions. 



Absence of formation of heat. 



Absence of decrement in wave. 



Low temperature coefficient of rate of conduction. 



No conclusive evidence of metabolism of any kind. 



