and Plants to the Electrical Phenomena associated vjith it. 43 



Hermann, have condemned it as an instrument of which the defects 

 are essential and irremediable. As I have answered these criticisms 

 elsewhere, I need only say here that for the investigation of the order 

 and duration of a rapid succession of electrical changes, such as those 

 with which we are now concerned, the instrument surpasses all others ; 

 and that by means of it my colleague, Professor Gotch, has with Mr. 

 Burch's aid, successfully photographed phenomena in nerve, of which 

 the very existence could not be demonstrated a few years ago.* 



The purposes to which we apply it are (1) for the measurement of 

 intervals of time between electrical changes which succeed each other 

 with great rapidity, and (2) the obtaining an estimate of their relative 

 intensities. The properties which make it so invaluable to us are 

 (1) that it responds to the action of a current promptly, beginning 

 when the current is closed, and indicating every change in its strength 

 or direction without measurable loss of time ; (2) that east. par., the rate 

 of ascent is proportional to the electromotive force of the current which 

 produces it ; and- (3) that the instrument can be graduated, and its 

 graduation verified by comparison with instruments of greater precision, 

 and thus used for the measurement of differences of potential of longer 

 duration. 



The diagrams 1, 2, and 4 illustrate the bearing of these three pro- 

 perties on the cases we have to investigate. As we shall see, a muscle 

 can be brought into action either by an instantaneous stimulus, by a 

 series of stimuli, or by continuous stimulation. Each of these has its 

 mechanical and its electrical response. I will anticipate so far as to say 

 that the three forms of electrical response correspond to the three 

 forms of mechanical. They correspond to the changes indicated by the 

 black lines in the three diagrams. I will further premise that all known 

 excitatory responses — all electrical changes which are concomitants of action 

 — may he compared with one of these types. 



Case 1. — Response to a continuous stimulation. A difference of 

 potential comes into existence at the contacts at the time t, and persists 

 long enough to produce its full effect on the column. (Diagram 1.) 



Case 2. — Series of short continuous stimulations. The column, 

 moves in alternately opposite directions. (Diagram 2.) 



Case 3. — Response to a single instantaneous stimulation. A differ- - 



* Full information relating to the instrument will be found in Mr. Burch's work 

 'The Capillary Electrometer in Theory and Practice,' and his papers in the 

 'Proceedings' (rol. 48, 1890) and 'Transactions' (A, vol. 183, 1892) of the Eoyal 

 Society. A very perfect method of recording the excursions of the electrometer 

 photographically and of interpreting the curves was described by Prof. Einthoven 

 in Pfiuger's ' Archiv ' in 1894, and applied by him to the investigation of the • 

 electromotive phenomena of the human heart. It need scarcely be added that the 

 two methods are the same in principle. An important paper has also recently 

 been published by Dr. R. du Bois-Reymond in the ' Archiv f . An. u. Physiol.,' 1898, 

 p. 516. 



