Carbon Dioxide From Nerve Fibres 109 



acids in the excited nerve, Waller still believes that it must give off 

 CO 2 when stimulated. In 1896, he showed, with an electro-physio- 

 logical method, that among other reagents, CO 2 , in minute quanti- 

 ties, increased the excitability of the isolated nerve of the frog, and 

 that the normal nerve, when excited, also increased its activity. 10 

 From this he ingeniously formed the hypothesis that every activity 

 in the nerve fibre must be associated with C0 2 production. 



That there may be CO 2 production in the nerve, but too small to 

 be measured by ordinary methods, is shown by the following calcu- 

 lations: A frog (Rana temporaria) gives off 0.355 gram of CO 2 

 per kilogram per hour at 19 20 C. 11 A small piece of the nerve 

 fibre of the same animal, say i cm. in length, will weigh in the neigh- 

 borhood of 10 milligrams. Now, if the mass of the nerve respires at the 

 rate of the whole animal, it would give off about 0.0000007 grams of 

 CO 2 during ten minutes. This calculation at once suggested that 

 the lack of positive evidence of metabolism in the nerve fibre was 

 not at all conclusive that such metabolism did not occur, in view of 

 the limitation of the methods for the estimation of C0 2 . It was 

 evidently necessary to devise methods for the detection of very 

 minute quantities of CO 2 . Thus at Professor Ma thews' suggestion 

 a new method for CO 2 analysis was first devised, and then, under, 

 his direction, I have undertaken to go back once more to the question 

 of CO 2 production in the nerve fibre during the passage of a nerve 

 impulse. 



To study the nature of metabolism involved in a tissue, one 

 should at least determine the oxygen consumption and the carbon 

 dioxide production. Inasmuch, as the present problem, however, is 

 concerned only with direct evidence for the existence of metabolism 

 in the nerve fibre, I have attempted to measure C0 2 production 

 only, for it is true that the lack of oxygen consumption may not 

 necessarily indicate the absence of chemical changes, while the pro- 

 duction of C0 2 will surely prove the presence of metabolism. Further- 

 more, as CO 2 production is the only sure universal expression of the 

 respiratory activity in anaerobic and aerobic plant and animal tissue 

 in normal condition, the inquiry of CO 2 production in an excited nerve 

 will not only concern the problem of the nature of the nerve impulse 



10 WALLER: Croonian lecture, Philosophical transactions, London, 1896. 



11 Taken from Pott's figures. See figures in Table ix, p. 129. 



