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 t 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- f carbon dioxide per 

 kilogram per hour at 19 to 20 C. A small piece of 

 the nerve fiber of the same animal, say i 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- f 

 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. 



