xl Obituary Notices of Fellows deceased. 



that the fact depends on the rate of subsidence, or, in the terms of 

 Nernst's theory, on the rate at which the concentration of ions brought 

 about by the exciting current is again dissipated by diffusion. A further 

 outcome of this point of view was the analysis of various excitable tissues 

 in the light of A. V. Hill's modification of Nernst's theory, in which 

 account is taken of the distance between the membranes at which the ions 

 concerned are supposed to be concentrated and of the diffusion constants of 

 these ions. The time-factor turned out to be in reality conditioned by these 

 two components of the expression deduced by Hill. An interesting point, as 

 yet not explained, is that the rates of movement of the ions in different 

 excitable substances differ more than those of the ordinary inorganic ions 

 known to be present. 



Since the rate of the excitatory process should be increased by rise of 

 temperature, it was natural to bring the different effects of temperature on 

 the apparent excitability of muscle and nerve to constant and indxieed 

 currents into connection with their optimal rates of incidence of energy. 

 The explanation was found to consist in two opposite effects of fall of 

 temperature. A fall of temperature means, on the one hand, a greater ease 

 of the production of the necessary concentration of ions, owing to the 

 decrease of opposing diffusion, while, on the other hand, the actual initiation 

 of the propagated disturbance is more difficult. The resultant effect varies 

 according to the duration of the current required to excite a particular tissue. 



The temperature coefficient of the rate of conduction in nerve was 

 measured by Keith Lucas, using an extremely accurate method. It was 

 found to be 1'79 for the 10 degrees between 8° and 18° C. 



For further progress it was necessary to make use of the electrical change 

 in excitable tissues as indicating the excitatory process. For this purpose 

 an improved form of capillary electrometer was invented, together with 

 apparatus for measuring the curves for the purpose of analysis. It was first 

 shown that the temperature coefficient of the rate of conduction in excitable 

 tissue is the same as that of the time of development of the electrical 

 disturbance. Hence there is no difficulty in taking this latter as the basis of 

 propagation of the excitatory state, although no proof of their identity is 

 given thereby. 



The next series of papers are de\'oted to the refractory period which 

 follows an effective stimulus. It was shown that the time which elapses 

 before an electrical change shows itself, when it is due to a second stimulus 

 following a previous one, is constant, although the time after the end of the 

 refractory period at which the second stimulus is given may vary con- 

 siderably. This fact suggested the name " irresponsive period " for the 

 interval between an electric response and the earliest possible succeeding 

 one. This delay occurs also in ventricular muscle, and is due entirely to a 

 modification of the tissue by the preceding propagated disturbance, and 

 not to any direct effect of the current used for stimulation. In conjunction 

 with his pupil, Bramwell, Keith Lucas next showed that the decrease of 



