upon the Elsctrotonic Currents of Medullated Nerve. 85 



(1) The weakest acid gives increased A. 



(2) Slightly stronger acid gives diminished A and increased K. 



(3) Still stronger acid gives diminished K. 



These statements are the outcome of a considerable number of 

 observations, and one may hardly hope to verify the progressive 

 action of acid from minimal to maximal in a single observation with 

 a single acid. Nor is it easy to give numbers in lieu of the indefinite 

 qualifications "weak" and "strong." This much may, however, 

 be said to give an idea of the order of magnitudes dealt with. 

 The second degree of change may be expected in consequence of 

 bathing the nerve for one minute in an acid solution of a strength 

 between N/20 and N/10. The free passage of " much " C0 2 into 

 the nerve-chamber usually affects the second degree of change in its 

 most typical form. A small amount of C0 2 , e.g., a few puffs of 

 expired air, will more probably affect the first degree of change. A 

 bath of one minute's duration in a N/5 solution of mineral acid will 

 almost certainly affect the third degree of change. A diminution of 

 K by C0 2 is rare {e.g., 2363). 



B. The Effect of Carbonic Acid and of Tetanisation. 



I have given particular attention to the action of carbon dioxide 

 and of tetanisation upon the A and K currents, in prosecution of 

 observations already reported concerning the action -currents of 

 nerve* and the influence of temperature upon the A and K currents. 



The usual and typical effects of carbonic acid are of the charac- 

 teristic acidic type, consisting in a diminution of A and an augmenta- 

 tion of K. 



Fig. 10— Action of C0 2 upon A and K (2422). 

 * ' Phil. Trans.,' B, 1897, p. 1. 



H 2 



