412 



THE PROPERTIES OF STRIPED MUSCLE. 



if, in preparing the muscle cylinder from a parallel-fibred muscle, the 

 fibres are cut obliquely, so that a section parallel to the long axes 

 of the elliptical cut surfaces is rhombic, the sharp and blunt edges 

 of such a rhombus are not equipotential, but the sharp edge is 

 relatively negative to the other, for a reason which the diagram 

 (Fig. 225) will help to explain. In an obliquely cut sectional surface, 

 the fibres are imbricated. In each fibre, a is negative to a, b to b\ 

 and so on ; for, as we have already seen, a more injured part is negative 

 to a less injured. The difference of potential ( a) between them is the same 

 in all. b is also negative to a, and c to b', and so on ; but this difference 

 is smaller than A by a certain amount (5), which is consequently the 

 difference of potential between a and b, b and c, and so on. And if the 

 cut surface is of the width of a hundred fibres, there will be a differ- 

 ence of potential of a hundred times the amount d between the two 

 borders. In other words, the ends of the fibres in an obliquely cut 

 surface act like voltaic elements in series ; whereas in a transverse 

 surface they act as if in multiple arc. These considerations help us to 

 understand the fact that the tendon end of the intact gastrocnemius is 

 ordinarily strongly negative to the middle. If the tendinous expansion 

 were not there, the relation of the exposed ends of the fibres would be 

 precisely that which has just been described in an obliquely cut surface. 

 Any part further from / would be negative to any nearer spot. 



Before proceeding to the study of 

 the excitatory response, it will be con- 

 venient to inquire, in a preliminary way, 

 whether the facts we have had before 

 us relating to the electromotive properties 

 of unexcited muscles — particularly those 

 relating to the equipotentiality of certain 

 muscles when sufficiently carefully pre- 

 pared, and to the readiness with which the slightest damage renders 

 any part of the surface, more especially in the neighbourhood of the 

 tendon, negative to the rest — can be comprehended under any general 

 statement. 



In any excitable organ two kinds of functional difference may exist 

 between parts. They may either have permanently differing functional 

 endowments, e.g. nerved and nerveless parts of the same muscles, or they 

 may be at the moment of observation in different states of fitness for the 

 discharge of function, this being clue to the circumstance that they are in 

 different stages of actual discharge of function or of exhaustion there- 

 from; or dependent upon injury, difference of temperature, or other 

 external conditions which affect function. It may be generally stated 

 as regards excitable organs, such as muscle and nerve, that in comparing 

 parts which are similarly endowed, those which are functionally in a more 

 capable state are positive to those which are functionally less capable. 

 No such " law " applies to organs which do not possess the property 

 of responding to stimulation. It appears to me impossible to 

 suppose that this fundamental difference between the one group of 

 organs and the other — those organs, namely, in which functional 

 activity has no concomitant electrical phenomena, and those, on the 

 other hand, in which this occurs without fail — should manifest itself 

 independently of the existence in the one set of organs of a special 

 mechanism which in the other set is absent. Nor can it be doubted 



Fig. 225. 



