374 MESSES. F. GOTCH AND V. HORSLEY 



The present series of experiments being planned for purposes of quantitative 

 measurement, the least complicated and most constant conditions were in all cases 

 selected, these being associated with careful isolation, and with the presence of one 

 electrode only in contact with the natural surface. It is probable that with these 

 conditions the total excitatory electrical change in the electrode circuit is chiefly that 

 produced by alterations affecting this one electrode. 



We will now proceed to describe the character of the movements of the mercury 

 when, with the capillary electrometer connected by the electrodes with an isolated 

 portion of cord, this structure is stimulated by a series of induction shocks alternate 

 in direction and following one another at intervals of y^ second (Helmholtz side- wire 

 inductorium). 



It has already been stated that one end of the " experimental tract " is prepared 

 for connection with the non-polarisable electrodes, the other for excitation ; so far as 

 the character of the effect revealed by the electrometer is concerned, it makes no 

 appreciable difference which end is respectively used for the purpose. In both cases 

 a minimal excitation evokes an electrical change in the other end of the tract which 

 affects the mercury of the electrometer, so that it moves rapidly up to a certain point, 

 and there remains steady without visible oscillation, while it falls on the cessation of 

 the stimulus, the mercury rapidly returning to its previous resting position. 



With more intense stimuli a larger excursion of the mercury is obtained, and 

 although no evidence of rapid vibration is detected, the character of the movement 

 often becomes irregular, rising and falling at intervals in a more or less abrupt 

 manner. 



Whilst then it was clear from its character that the movement of the mercury is in no 

 way connected with any electrotonic or other escape from the exciting circuit, since 

 there is no evidence of rapid rhythmical alternating effect, synchronous with the 

 number of stimuli, it was desirable to ascertain to what extent the irregularities just 

 referred to were true indications of changes in the cord. 



To ascertain this, experiments were made in which (see fig. 1 1 ) the cord was divided 

 at one point only, the 8th dorsal, and the upper end of the lower fragment connected 

 with the electrometer. The rectus femoris muscle was then prepared as indicated in 

 the preceding paragraphs dealing with the transmission time (p. 366), but the attached 

 ligature was fixed to a strong spring (FiCK's isometric myograph), the movements 

 of which, as recorded by a lever, were magnified 50 times. The cord was then exposed 

 in the lumbar region and its lateral surface excited, the muscular contractions were 

 observed and recorded, and at the same time the character of any displacement of the 

 mercury of the electrometer was ascertained as far as possible by the eye, and roughly 

 drawn upon paper. 



It was thus ascertained that the electrical effects in the dorsal region of the cord 

 evoked by lumbar excitation, and evidenced by the mercurial movements, coincided 

 in plan and character with the muscular effects. 



