EXCITATION AND TRANSMISSION 71 



that excitation, even in the nerve fiber, is accompanied 

 by increase in CO 2 production and holds that irritability 

 and excitation in general are associated with oxidative 

 metabolism. 



Bayliss and Lucas have criticized these conclusions 

 on the ground that Hill (1912) has been unable to dis- 

 cover any appreciable heat production associated with 

 the transmission of the nervous impulse, and have 

 pointed out the possibility that the C0 2 produced by 

 nerves may be dissolved in the tissues, and that its 

 increase on electrical stimulation may be due to the 

 rise in temperature occasioned by such stimulation. 

 The demonstration by Tashiro and by Riggs (1919) 

 that chemical stimulation, as well as electrical stimula- 

 tion, is accompanied by increase in CO 2 appears to 

 an^ver this objection. But whatever the situation may 

 prove to be in the highly specialized excitatory process 

 in the nerves of higher animals, there seems to be no 

 doubt that protoplasmic excitation in general involves 

 metabolic and particularly oxidative reactions. Excita- 

 tion in its most primitive form apparently involves in 

 one way or another an acceleration in the fundamental 

 activities of living protoplasm, particularly those con- 

 cerned in the liberation of energy. 



In a series of papers R. S. Lillie 1 has developed a 

 general theory of excitation and transmission based on 

 extensive experimental evidence and in terms of current 

 physicochemical conceptions. Since this theory is con- 

 cerned to some extent with the process of excitation and 

 transmission in general and not merely with the process 



1 R. S. Lillie (19090, b, c, 1911, 1913, 1914^ ^S, 19160, b, 1917, 

 1918, 1919), R. S. Lillie and E. N. Johnston (1919). 



