ELECTRO-PHYSIOLOGY 637 



they are related to the functional activity of the tissues. It is, of 

 course, clear that energy must be transformed to produce an electro- 

 motive force capable of doing work. It may be assumed that this 

 energy is ultimately derived from the stock of chemical energy in 

 the tissue-substance. But whether in the final transformation the 

 electrical phenomena are the expression of chemical changes or of 

 physical changes, or of both, we do not know. Bernstein has sup- 

 posed that in the chemical process, whose visible outcome is a 

 muscular contraction, there are three stages: (i) The liberation of 

 (intra-molecular) oxygen from the molecules of the living substance, 

 and its appearance as active or atomic oxygen (p. 362); (2) Oxida- 

 tion of the contractile substance by this oxygen ; (3) The assimila- 

 tion of oxygen by the contractile substance /.*., its passage into the 

 inogen molecules (p. 247). According to him, it is the first of these 

 stages which is associated with the abrupt development of the 

 difference of potential between the excited and unexcited por- 

 tions of the muscle which we call the negative variation. This first 

 stage he assumes to be completed before the visible contraction 

 begins ; and he originally asserted that the same was true of the 

 negative variation. It is now known that the latter, although it 

 begins before the contraction, and very rapidly reaches its maximum, 

 declines more gradually, so that it overlaps the mechanical change 

 of form. This is particularly well seen in veratrinized muscles 

 (p. 569), in which the electrical variation, like the contraction, is 

 greatly prolonged (Garten). Nevertheless, Bernstein's theory, even 

 with this limitation, agrees with what is known as to the influence 

 exerted on the negative variation by the mechanical conditions of 

 the contraction. For the electrical change is little, if at all, affected 

 by the tension of the muscle or the load it has to lift ; and this is 

 what we should expect if it depends on a process which is mainly 

 completed before the contraction begins. There are, however, 

 certain facts which warn us against too confidently associating the 

 negative variation with any absolutely essential step in the excitatory 

 process. In regenerating nerves, apparently normal nerve impulses 

 can be set up and propagated without any perceptible electrical 

 variation. And Gotch and Burch sometimes found that in nerves 

 kept (in normal saline solution made with tap-water) for twenty-four 

 to forty-eight hours before observation, two electrical variations could 

 ' be obtained in response to two successive stimuli from one part of 

 the nerve, and only one from another an anomaly which, since the 

 physiological condition of the nerves was known to be very uniform, 

 they could only explain by supposing that in the part of the nerve 

 which showed only one variation the second excitatory process, 

 although normally propagated, was not accompanied by a separate 

 electrical change. 



Physical explanations of the action current of muscle have been 

 based on the hypothesis that in contraction variations in surface- 

 tension, with accompanying electrical changes, occur at certain 

 surfaces (surface of separation between light and dim discs, or 

 between fluid contents and wall of sarcous capillary tubes). A great 



