A. R. MOOEE 615 



end-point was determined by matching the experimental tube with 

 another containing a solution having a tint corresponding to pH 

 7.4. The matching was done by diffuse daylight or by the light 

 of a daylight lamp, and the time taken with a stop-watch. The 

 experimental error is not over 10 per cent. Obviously the method 

 measures only the rate and not the absolute amounts of carbon 

 dioxide produced. But since the metabolism of nervous tissue is 

 of the greatest significance when compared with that of other tissues, 

 and since the problem of stimulation is entirely a question of com- 

 parative rates, any attempt to determine absolute values is, for us, 

 beside the point. 



Some of the earlier workers^ in attempting to determine the re- 

 action of nerve substance to indicators had found the cut surface of 

 the gray matter in the brain and cord to be acid to Utmus and other 

 indicators. I have shown that the brain, cord, and sciatic nerves 

 of frogs upon being cut or crushed give an acid reaction with phenol- 

 sulfonephthalein.^ If the sciatic nerve of a frog is kept for half 

 an hour in alkahne (pH = 8.0) Ringer's solution saturated with the 

 indicator, the nerve takes up some of the stain and appears pink, 

 except at the cut end where it is yellow; viz., acid. Microscopic 

 examination shows that the cut end of each fiber is yellow. If the 

 stained nerve is crushed on a glass plate with a glass rod, the entire 

 tissue turns yellow. The same result follows if the nerve is allowed 

 to dry in the air or in C02-free air, while neutral cotton tinted with 

 the indicator and treated in the same way shows no change in re- 

 action. This acid of injury is not due to stimulation, since it is 

 strictly localized at the points of cutting or crushing. 



It can be shown that all the acid given off by nervous tissue and 

 the greater part of that given off by muscle is carbon dioxide. For 

 this purpose the tissue is put into a tube of tinted Ringer's solution 

 previously freed from carbon dioxide by aspirating with C02-free 

 air. When a certain amount of acid has been formed, the tissue is 

 removed and the solution again aspirated with C02-free air. This 

 treatment removes all the acid formed by nervous tissue, as shown 



^Pfliiger, E., Arch. ges. Physiol., 1875, x, 312. 



9 Moore, A. R., Proc. Soc. Exp. Biol, and Med., 1917-18, xv, 18. 



