74 A CHEMICAL SIGN OF LIFE 



more carbon dioxide. If we are to assume the second 

 possibility, we must inquire why one portion should die 

 earlier than the other. The fact that an isolated nerve 

 stays excitable for a considerable period of time makes 

 this interpretation quite untenable, although we support 

 the idea set forth by Child that the death gradient is 

 directly associated with the metabolic gradient. It 

 may be added here that death modifies the carbon 

 dioxide production gradient. 



Whatever interpretation we choose, inasmuch as we 

 contend that the rate of metabolic activity as measured 

 by the carbon dioxide output is a function of the irri- 

 tability, we are assuming that there must be different 

 rates of metabolism along the normal nerve fiber. 

 Not only that such an assumption is correct, but also 

 that the effect of injury and death are only secondary 

 and minor factors, can be shown in the light of Child's 

 experiments when the same nerve was examined, result- 

 ing in the confirmation of our results by an entirely 

 different method. 



He has shown that in various concentrations of potas- 

 sium cyanide, from o.ooi to o.oi molecular in strength, 

 the fibrillae of the claw nerve of the spider crab after a 

 time become irregular in outline and more or less vari- 

 cose, so that a strand appears more or less granular in- 

 stead of fibrillar, like a fresh nerve. With this criterion 

 he has discovered a gradient similar to our metabolic 

 gradient, which appears in the structural death changes. 

 Using a i per cent ethyl ether solution in sea-water, or 

 even a somewhat lower concentration, he found that 

 the change from fibrillar to granular appearance begins 

 at the ends of the nerve very soon after it is brought into 



