636 A MANUAL OF PHYSIOLOGY 



in glands during secretion, in the central nervous system 

 during the passage of impulses along its conducting paths. 

 Some of these will be further considered a little later on. 



As to the interpretation of the facts we have been de- 

 scribing, and which are summed up in the three propositions 

 on p. 629, two chief doctrines have divided the physiological 

 world : (i) the theory of du Bois-Reymond, the pioneer of 

 electro-physiology, and (2) the theory of Hermann. It was 

 believed by du Bois-Reymond that the current of rest seen 

 in injured tissues is of deep physiological import, and that 

 the electrical difference which gives rise to it is not de- 

 veloped by the lesion as such, but only unmasked when the 

 electrical balance is upset by injury. He looked upon the 

 muscle or nerve as built up of electromotive particles, with 

 definite positive and negative surfaces arranged in a regular 

 manner in a sort of ground-substance which is electrically 

 indifferent. The * negative variation ' he supposed to depend 

 on an actual diminution of previously-existing electromotive 

 forces ; and from this conception arose its historic name. 

 This theory has been highly elaborated and extended to 

 include new facts as they have arisen. But although it 

 explains certain phenomena, such as the currents of a prism 

 of muscle, better than the simpler theory associated with the 

 name of Hermann, most physiologists have now abandoned 

 it in favour of the latter. Hermann and his school assume 

 that the uninjured muscle or nerve is ' streamless,' not 

 because equal and opposite electromotive forces exactly 

 balance each other in the substance of the tissue, but 

 because electromotive forces are absent until they are called 

 into existence at the boundary, or plane of demarcation, 

 between sound and injured tissue. For this reason in the 

 terminology of Hermann du Bois-Reymond's current of rest 

 is called the ' demarcation ' current. 



Relation between the Negative Variation and Functional Activity. 

 Although the negative variation is so general an accompaniment 

 of excitation, and is even within tolerably wide limits, in muscle and 

 nerve at least, pretty nearly proportional to the strength of the 

 stimulus, it is at present impossible to say definitely what the 

 chemical or physical changes are which underlie it, nor how closely 



