1 66 COMPARATIVE ELECTRO-PHYSIOLOGY 



patches may be quite dark and discoloured, while, as the 

 living tissue is approached, this dark passes imperceptibly 

 into yellow colour. And beyond this, again, we find the 

 discolouration of yellow passing into the vivid green of living 

 tissue. Proceeding thus in a radial direction inwards, towards 

 the centre of such a patch from the living green, we shall 

 find all possible stages of death, from its initiation, somewhere 

 on the border-line between green and yellow, to its phase of 

 completion, in the dark central area. On testing the electrical 

 conditions of these different parts, I found that the border 

 between green and yellow was negative to the living green 

 surface. But the same point was also negative to the dead 

 central area, and more negative to this than to the living 

 tissue. Hence the dead was relatively positive to the living. 

 Or if we make one fixed contact on the living tissue, and 

 if the second exploring contact be made with various points 

 successively on a radial line passing from this to the centre 

 of the dead area, these contacts will pass in succession through 

 the living, the dying, and the dead. The variation of elec- 

 trical potential will be found to be at its greatest along this 

 line. The electro-motive difference between the point which 

 has been fixed on the living tissue, and the exploring second 

 contact, will at first be found to increase. The maximum 

 difference is attained on reaching the border-line between 

 green and yellow, or very little beyond this, this point being 

 galvanometrically the most negative. On now passing further 

 inward from this point, the maximum difference is found to 

 decrease, till we come to a point in the dead tissue which is 

 iso-electric with the living. On now again passing inwards, 

 to the still more completely dead tissue of the central area, 

 we find that we are approaching points which are more and 

 more galvanometrically positive, as compared with the living 

 tissue. The dying point on the border-line between green 

 and yellow is thus the most negative, and points to the right 

 or left of this are positive in comparison with it, the dead, 

 however, being more positive than the living. It has been 

 said that the electro-motive variation is most rapid along the 



