414 



THE PROPERTIES OF STRIPED MUSCIE. 



in which the word " negative " is used in its algebraic, not in its electrical 

 sense. The transitory change which corresponds to the single contrac- 

 tion is of very short duration, and is propagated in such a way that 

 by the time it reaches the end of a muscle furthest from the seat of 

 excitation, it may have already ceased in the neighbourhood of the 

 excited part. This being so, it is not difficult to understand that 

 the response to instantaneous stimulation remained unrecognised for 

 many years after the electromotive properties of muscle in the resting 

 state and the " negative variation " (in the original sense of du Bois- 

 Eeymond) were well known. 



Whereas the " negative variation " is persistent and not propagated, 

 the response to instantaneous stimulation is transitory and spreads at a 

 rate of many feet per second. In both cases the change manifests itself 

 by relative electrical negativity of the affected part of the surface. In 

 discussing these changes, it is necessary to bear in mind the caution 

 already given, that the phenomena observed are those of the instruments 

 we employ rather than those of the organs we explore. If we talk of 



" action currents," 

 I 



we refer to currents 

 as they really exist 

 in the galvanometric 

 circuit; if we say 

 that a certain spot 

 is " negative," we 

 mean that there is 

 a difference of poten- 

 tial between the 

 surface of contact 

 to which we refer, 

 and another contact 

 surface to which the 

 other electrode is 

 applied — which dif- 

 ference we measure 

 either by the com- 

 pensator or the elec- 

 trometer. 



(a) The elec- 

 trical response to 

 an instantaneous 



Fig. 226. — Bernstein's differential rheotoine. 



stimulus — Its time-relations. — It was known from an experiment made 

 by Helmholtz, which will be referred to further on (p. 421), that the 

 electrical response to an instantaneous excitation is of very short 

 duration, and that it precedes the change of form. But it was not 

 until twenty years later that Bernstein devised a method for investi- 

 gating its time-relations, and particularly its rate of propagation, and 

 was further enabled to distinguish the differences between the phenomena 

 of the electrical response, as they present themselves in injured and in 

 uninjured muscles respectively. The description of the instrument, 

 which he called a Differential Rhcotome, is now to be found in most text- 

 books. It will be sufficient, therefore, to refer to the original diagram, 

 which is reproduced in Fig. 226. l 



1 From Bernstein's "Lehrbueh der Physiologie," S. 354. 





