314 Mr. J. S. Macdonald. 



5. Selecting one cross section and systematically measuring the 

 E.M.F. available between this and points on the longitudinal surface, 

 drawing a complete curve (force diagram) at regular intervals of 30' 

 between each curve, the levels of the curves fall with diminishing 

 rapidity, and a gradual change occurs in the form of each curve. 



After the nerve has been removed some hours from the animal, the 

 maximum E.M.F., the highest point of the curve, may have sunk to 

 one-tenth of its original value. If now the nerve is taken and placed 

 for a short period (five minutes) in tap water, a maximum E.M.F. ia 

 obtained considerably greater than the maximum obtained from any 

 point of the same nerve when freshly removed from the recently-killed 

 animal. If the value of the demarcation source is taken as an index 

 of the condition of the nerve, then a rejuvenation has taken place 

 with the immersion in tap water. 



This increased value remains for some time, the curve being of not 

 much different form, and the rate of fall of level being similar to the 

 rate of fall from the original maximum. If the nerve be left in tap 

 water for twenty-four hours, a demarcation current, a difference of 

 potential between each point on the longitudinal surface and the cross 

 section is observed, giving a curve very similar to that obtained after 

 the first immersion in tap water twenty-four hours previously. 



If one waits after the death of an animal until rigor mortis is com- 

 pletely established, and a nerve be then removed, only a small trace 

 of demarcation current is obtainable from it, and the curve of E.M.F. 

 due to a cross section is at an extremely low level. If now this nerve 

 is left for a short period (five minutes) in tap water, a maximum 

 E.M.F. is obtainable from it higher than that obtained from the fresh 

 nerve of the recently-killed animal, and as high as that obtained after 

 the immersion of the fresh nerve in tap water, and there is no marked 

 difference in the form of curve (force diagram). 



If a nerve is removed at once after the death of an animal, and the 

 E.M.F. between a "maximal" point and the cross section is taken 

 (1) immediately (2) after a short immersion in 0'9 per cent, saline, 

 then it is seen that the 0*9 per cent, (normal) saline has diminished the 

 E.M.F. If the nerve be now immersed in 0'45 per cent, saline the 

 original value is returned, and is increased by a further immersion in 

 0'3 per cent., - 2 per cent., O'l per cent, saline solution, each further 

 dilution increasing the E.M.F. A return of the nerve through the 

 series diminishes in each case the E.M.F., to be renewed by a sub- 

 sequent return to the weaker solution. 



The maximum effect is obtained by the action of tap water, and a 

 very considerable reduction of this maximum is obtained by a sub- 

 sequent immersion in O'l per cent, saline, to be followed by a return to 

 the maximum with a return to the tap water. 



There is no sign of any critical point marking the separation of two possible 



