Physiology. — "TJie lueasmeinent of Chroi)ft,rla\ By Prof. J. K. A. 

 Werthp:i.m Sat.omgnson. 



(Communicated in llie meeting of March 29, 1919). 



Hoohweg's law tor the stimulation of" excitable tissues by means 

 of electric cnrrents stale.s thai the rate of excitation rapidly lessens 

 during the flow of the cnrrent. His law may be mathematically 

 expressed by 



_V = a { <l{t)t -^'dt (1) 







if // represents the excitation cansed by a current / = (f{tj, n and ^ 

 being constants. Hookweg calls n the initial constant, ,:? the extinction 



constant. The reciprocal of the latter is generally called the time 



i' 

 constant of the stimulated tissue. Lapicque introduced the word 

 chronaxia to designate this time constant. 



The measurement of the chronaxia is of the greatest importance 

 if we wish to indicate the excital)ility liy electricity of the animal 

 tissue. According to Doumek we can calculate it from the results of 

 three condenser discharges under definite conditions. Hoorweg proposed 

 two condenser discharges and one stimulation with the direct 

 constant current, which for a long time has been the only available 

 method. Cluzet uses a series of discharges of condensers of different 

 capacity and calculates the chronaxia fiom the one in which the 

 smallest amount of electrical energy was needed to obtain a minimal 

 contraction. Lapicque has published a method for directly measuring 

 the chronaxia with the direct current, closing and opening the circuit 

 with two rapidly working contact keys of an instrument called a 

 chi-onaximeter. ^. similar method was used by Keith, Adrian and 

 others. I worked out a method in which a calibrated induction coil 

 was used. 



In all these measurements we find not only the chronaxia, but 

 also the rheobasis, a constant which received this name from 

 Lapicque. It is the smallest direct current causing a minimal muscle 



twitch, and is equal to the quotient of Hoorweg's constants -. 



