PROPAGATION OF PHYSIOLOGICAL CHANGE 491 



process such as is attended with a consumption of oxygen, nor 

 with the transit of oxygen from less stable to more stable 

 combination. And this is equivalent to saying that, whereas 

 oxygen may play a considerable part in the maintenance of the 

 normal state of nerve, it plays no part in its function. We are 

 obliged, therefore, to consider the case of nerve apart from the 

 case of muscle, where each functional display is attended with a 

 production of heat and a discharge of carbonic acid. But is 

 this statement as true as it at first sight appears ? In muscle 

 function there are two clearly separable phenomena, the pro- 

 pagation of an electrical change and the consequent contraction. 

 The propagation of electrical change is undoubtedly a process 

 of the same rank as the process studied in nerve. With regard 

 to this moiety of muscle function wherein muscle resembles 

 nerve, there is likewise no evidence of any production of heat 

 or output of waste product. The electrical change is over 

 before the occurrence of that functional display which is usually 

 thought to be associated with these factors. In the case of 

 muscle, when acting as nerve, the facts are obscured by a later 

 exhibition of another function. In the case of nerve itself 

 the facts are clear. There is nothing but an electrical change 

 observable. 



It is not marvellous in view of such evidence that investigators 

 have been found bold enough to plan a line of experimental 

 attack upon the mysteries of nerve function, based primarily 

 upon the assumption that the materials present in nerve are 

 important solely as conductors, insulators, dielectrics. This is 

 a very different assumption from that underlying the " biogen 

 molecule," and yet in this case it has proved of the utmost value. 

 If the purely physical concept of nerve function is finally 

 set on one side, it will be set on one side as the result of 

 evidence collected upon these lines. Some of this evidence 

 has favoured such a concept, some of it has served materially 

 to limit its range. The peculiarities of the electrical conductivity 

 of nerve have been closely studied, sometimes deliberately, 

 sometimes as a series of data which would one day acquire 

 biological interest in connection with the characters of proto- 

 plasm. Both sets of workers have used the same methods. 

 An electrical current is passed through a nerve and data are 

 collected from the " polarised " region as also from the extra- 

 polar stretches. For instance, in the anodal extrapolar region 



