Page:Proceedings of the Royal Society of London Vol 69.djvu/199

Rh FIG. 14

B C A

Excitation.

i i i

Bight foot. 12 hours. 4 L. 1000 +

12i liours. 4 L. 10,000 +

OOI

nil/.

OO4

-O05

Response ingoing at B.

A.

Ri-sponse outgoing at B.

After this series of four trials at 10,000, a, series of four trials at 1000 gave no effect. On transfer of an electrode to fresh pad an ingoing response was observed after excitation at 1000.

The longest period at the end of which I have detected unmis- takable physiological response of a surviving pad has been 7 days post mortem. I have not, however, sought to follow out the reaction to its last remaining trace so as to determine a maximum duration of survival, because with declining voltage of reaction the disturbing effects of polarisation counter-currents become more and more appx- rent. At a comparatively early period the response to single shocks disappears, and the galvanometer, if sensitive, manifests only polari- sation effects contrary in direction to the test shocks. At this period tetanisation by currents alternating in direction will still bring out a true summated outgoing effect with both pairs of direc- tions of currents ; under these conditions the effect of polarisation is relatively smaller. But at a later period, as the life of tissue is coming to an end, and the response reaches a value to be measured in ten thousandths of a volt, the disturbing influence of polarisation again becomes apparent. In this case the deflection after tetanisation is reversed with reversal of direction, and a resultant due to superior polarisation by make is witnessed in the direction of break. The shortest period after death at which I have observed this state has been