1912.] The Process of Excitation in Nerve and Muscle. 507 



proposition that the electric response is a constant concomitant of the 

 propagated disturbance. But for the purpose of any hypothesis as to 

 the physico-chemical nature of the latter, the mere stringent proof of that 

 proposition would not be enough. The important point for any such 

 hypothesis is whether they are identical, that is whether the disturbance 

 of electric potential at one point on a nerve is the actual and direct cause of 

 the same phenomenon in a neighbouring part. Any hypothesis must be 

 prepared to state whether the electric phenomena play the central part in 

 propagation or are to be relegated to the position of a mere by-product. 



On this point it is hardly likely that the direct experimental method can 

 decide. A more hopeful line of enquiry springs from the study of that local 

 excitatory process whose recognition was the first step in this analysis. If 

 we can satisfy ourselves as to the physico-chemical nature of the local change 

 we shall know the conditions by which the propagated disturbance is initiated, 

 and we shall have some ground for hypothesis as to the change which would 

 need to be produced by the propagated disturbance in one part of a nerve 

 in order that a like change might spread to the neighbourhood. To this point 

 I shall return. 



There is one more line of experimental work upon the relation of the 

 electric response to the propagated disturbance which must be taken into 

 account before we pass to the remaining steps of the analysis. Though the 

 general fact of the association of the electric response with the propagated 

 disturbance is already established clearly enough, yet there is evidence 

 pointing to a modification of the electric response by the mechanical 

 conditions of contraction in a muscle. Amaya,* Bernstein and Tschermak,t 

 and more recently Samojloff,t have called attention to alterations of the 

 electric response consequent on the tension encountered by a muscle during 

 contraction. These facts may have no more significance than an alteration 

 of the electric conductivity of a muscle during contraction. They may, how- 

 ever, touch our argument more closely in the sense that, as Straub§ has 

 recently suggested in the course of work on the heart, some small part of 

 the electric response of muscle may have its origin in chemical processes 

 related to contraction. This possibility needs to be kept in mind even though 

 the general origin of the electric phenomena in nerve and in muscle can 

 scarcely be supposed to differ. 



* Amaya, 'Arch. f. d. ges. Physiol.,' 1898, vol. 70, p. 101. 



t Bernstein and Tschermak, 'Arch. f. d. ges. Physiol.,' 1902, vol. 89, p. 289. 



+ Samojloff, ' Arch. f. (Anat. u.) Physiol. Suppl.,' 1908, p. 1. 



§ Straub, ' Zeitschr. f. Biol.,' 1910, vol. 53, p. 499 ; cf. also Samojloff, ' Arch. f. d. ges. 

 Physiol.,' 1910, vol. 135, p. 446. 



