14 A CHEMICAL SIGN OF LIFE 
induction shock, he obtained a series of electrical 
responses, each of which is the greatest the nerve can 
give at the time, but each of which is a little greater 
than its predecessor. Such a series of increasing re- 
sponses is known as a staircase, the negative phase 
increasing steadily while the positive phase decreases. 
This Waller explained by supposing that small amounts 
of carbon dioxide were formed by each nerve activity, 
and that this augmented the negative response and 
diminished the positive response, just as does carbon 
dioxide applied to the outside of the fiber. He considered 
that our failure to find the gas was due to the inadequacy 
of the chemical methods then in existence. That this 
criticism of Waller’s was a just one and that there may 
be carbon dioxide produced by nerves, but too small in 
amount to be measured by the ordinary chemical method, 
is shown by the following calculation: A frog (Rana 
temporaria) gives off 0.355 g. of carbon dioxide per 
kilogram per hour at 19° to 20° C. A small piece of 
the nerve fiber of the same animal, say 1 cm., or three- 
eighths of an inch, in length, will weigh, probably, not 
more than 10 mg. Now, if this mass of the nerve 
fiber respires at the same rate as the whole animal, it 
will not give off more than about 0.000,000,7 g. of 
carbon dioxide during ten minutes. This calculation 
at once suggested that the failure to detect the evolution 
of carbon dioxide in nerves was very probably due to the 
limitation of the methods for the estimation of the carbon 
dioxide, and that it was not at all conclusive evidence 
that carbon dioxide was not produced. It was evidently 
necessary to devise methods for the detection of very 
minute quantities of carbon dioxide. 
