CURRENT OF INJURY AND NEGATIVE VARIATION 163 



recovery from a strong stimulus is very protracted. Hence, 

 after such stimulation, there is persistent galvanometric 

 negativity as an after-effect. As the intensity of this after- 

 effect depends upon the intensity of stimulation, it will be 

 seen that the galvanometric negativity near the section will 

 be greater than at a distant point, where the transmitted 

 effect of stimulation is feeble. From this it follows, that the 

 so-called current of injury will flow in the tissue from the 

 neighbourhood of the cut, to the distant and relatively un- 

 excited end. The current of injury is thus an after-effect of 

 strong stimulus. The peculiar electrical distribution which 

 occurs in a muscle-cylinder is also found in a plant-cylinder, 

 and both are equally explicable from the fact that the 

 greatest excitatory after-effect occurs at the two sectioned 

 ends, and that this decreases progressively towards the 

 equator. The over-stimulated area of injury has its excit- 

 ability depressed or abolished; diffuse stimulation, causing 

 greater excitation of the uninjured contact, induces in it a 

 greater excitatory effect of negativity, and this gives rise to a 

 diminution of the existing difference of potential, as between 

 the injured and uninjured. This is the explanation of 

 response by the so-called negative variation. 



In an anisotropic tissue the excitation caused by injury, 

 when diffused, induces greater galvanometric negativity of 

 the more excitable part. If this be the distal end, the re- 

 sultant persistent current will be from the distal uninjured to 

 the proximal injured. An apparently anomalous case will 

 thus arise of a ' positive ' current of injury, so-called. 



M 2 



