68 



ANIMAL ELECTRICITY. LECTURE III. 



after-effects. Remembering that the characteristic 

 effect of CO2 from without, and presumably from 

 within, Is an augmentation of negative response and 

 a diminution of positive response, we have no diffi- 

 culty in admitting that the electrical staircase of nerve, 

 whether ascending or descending. Is brought about by 

 carbonic acid evolved at each step in a series. It is 

 pretty obviously a CO^ phenomenon. 



Fig. 32. — "Staircase" of contractions 

 of a frog's heart. 



iifflfflii^ 



Fig. 32 A. — "Staircase" of electrical responses of nerve. 



Staircase effect, then, is not confined to contractile 

 tissue, it clearly applies to nerve where it is equally 

 clearly produced by CO^. To my mind this precise 

 notion is a welcome addition to ouf somewhat less 

 definite psychological notions concerning staircase 

 effects obtaining In central nervous action. 



Summation of stimuli — i.e., the gradual accumu- 

 lation of a series of individually Insufficient stimuli 

 into an effective excitant — is itself conceivable as the 

 expression of augmenting excitability by augmenting 

 evolution of CO^. The establishment of paths of less 



