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 0.001 too.o1 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 1 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 
