Page:Proceedings of the Royal Society of London Vol 60.djvu/413

386 Electrotonic after-currents, A' and K', when present to any marked degree, are opposed to the previous electrotonic currents A and K. Designating A and K respectively as positive and negative, the after-currents A' and K' are respectively negative and positive. Such after-currents are in general modified by previous rise of temperature, which gives rise to an evident A' (negative) in a nerve which previously gave no marked A', and abolishes a K' (positive) that may previously have been present. Experiment 2366 exhibits the development of an evident negative A' subsequent to heating of the nerve. Experiment 2322 exhibits the abolition of a positive K', evident previous to heating of the nerve.

A fall of temperature causes an increase of the A current and, in less degree, of the K current; by reason of the diminution of resistance that takes place with lowered temperature, the increase of A is more marked than is apparent upon the record, and the smaller increase of K is quite masked by the diminution of resistance. The quotient A/K is augmented. At a temperature of —4° to —6° both currents are somewhat suddenly abolished; this abolition may be complete and final, no recovery taking place, or it may be temporary, being succeeded by imperfect recovery as the nerve temperature returns towards normal. It is noteworthy that the A and K currents are not abolished at 0° suddenly, and all but finally abolished at —4°