CHEMICAL SIGNS OF IRRITABILITY 33 



duction per gram is reduced thereby. But one thing 

 seems to be certain, i.e., that to attribute the carbon 

 dioxide production in the nerve fiber to the connective 

 tissue cells surrounding the nerve trunk, as Bayliss does, 

 is rather ridiculous. Nerve cells evidently breathe 

 at about the same rate as nerve fibers, and not faster, as 

 one might suppose. Table IV summarizes the carbon 

 dioxide production by various nervous tissues, some of 

 which contain cells and others only fibers. 



Summary. We have thus far shown, then, that the 

 living nerve fiber is no exception to the rule that all 

 living matter undergoes chemical changes. It respires. 

 There is a chemical sign of irritability in the nerve. 

 By the use of a proper apparatus of sufficient delicacy 

 we can demonstrate experimentally the formation of 

 carbon dioxide in all nerves; and by estimating the 

 amount produced under various conditions conditions 

 which we know affect the state of irritability of the 

 normal nerve in the body we find a very close parallel- 

 ism between the amount of carbon dioxide produced and 

 the state of irritability. We are justified, therefore, in 

 concluding that the gas thus measured is the expression 

 of the metabolic activity of the nerve. We may now 

 pass on to discover whether this carbon dioxide is 

 increased in case of stimulation. 



