150 Di'' «/. Burdon- Sanderson [June 9, 



the excitatory process in muscle, a knowledge of which is essential to 

 our purpose. 



The first of these is, that in every such process the visible 

 response (in the case of muscle the contraction) is separated in time 

 from its cause, the excitation, by a period during which no visible 

 change occurs, although, for reasons which I need not here insist on, 

 molecular changes must be in progress. With suitable appliances it 

 would not have been difficult to prove this to you experimentally in 

 respect of ordinary muscle, but it can be much more easily demon- 

 strated if I substitute for ordinary voluntary muscle, the muscular 

 tissue of the heart, in which the process is about fifteen times as slow. 

 Here, although the excitatory changes occur in the same order, and 

 are of the same nature as in common muscle, the interval between 

 excitation and response, amounting to about a sixth of a second, is 

 very easily perceived.* 



It is obvious that this interval may be regarded as a period of 

 transition from the quiescent to the active state, and I told you at the 

 beginning of the lecture that it was always accompanied by electrical 

 changes of a characteristic kind in the excited part. I wish now to 

 show you, that in the muscular substance of the ventricle of the 

 heart, in which we have been able to observe the existence of an 

 interval of apparent inactivity between excitation and visible resi^onse, 

 this transition-time is occupied in the way that has been stated. 

 For this purpose we have arranged the ventricle of the heart of a 

 frog in such a way that it can be projected on the screen. At the 

 same time the surface of the ventricle is led off to the galvanometer, 

 the electrodes being applied one at the base the other at the apex. 

 The galvanometer is so arranged that the image is thrown on the 

 screen close to the lever. On exciting the heart as near as possible 

 to the apex, the image shoots off in a direction which indicates that 

 the excited part of the surface of the ventricle becomes negative to 

 the rest, and it is seen at the same time with perfect distinctness that 

 the electrical effect precedes the mechanical, i.e. the rise of the 

 lever. 



There are two other facts which are of importance for our purpose, 

 and for the demonstration of which the muscular tissue of the 

 ventricle of the heart of the frog is also available. The first is that 

 during a certain period after each excitation, which M. Marey has 

 called the " refractory period," but which is more correctly termed the 

 period of diminished excitability, the tissue does not respond to a 

 second excitation : the second is, that the duration of the excitatory 

 effect (as indicated by that of the electrical disturbance of the 



* For this purpose the conical ventricle of a frog's heart was projected on the 

 screen with a weight attached to its apex, the base being fixed. It was excited 

 directly by an induction shock, an electro-roagnetic indicator, interpolated in the 

 primary circuit of the inductoriuni being also projected. The interval of time 

 between the two events, viz. the induction shock and the response, was made 

 obvious. 



