100 
MR. G. J. BURCH ON THE TIME-RELATIONS OF THE 
machine. The slight notch about the middle of the descent, indicates a “ sticky ” 
place in the capillary. (Compare fig. 7.) # 
A companion photograph, in which the excursion was upward, did not develop 
sufficiently dense to print, but was similar in character, the upward overshooting 
being very slight. 
These photographs show, that without external resistance in the circuit, the effect of 
overshooting, and especially of that form of it which is due to the elasticity of the 
meniscus, interferes seriously with the application of this method of analysis, unless the 
differences of potential concerned are small, but that these difficulties vanish on the 
introduction of a moderate resistance, not sufficient to make the movements of the 
electrometer sluggish. With suitable precautions, the variations of a difference of 
potential may be determined for each two-thousandth part of a second, and under 
favourable circumstances, with an error of not more than one per cent. 
Part II. 
Application of the Method to the Study of the Electrical Variations of Muscle. 
In a paper by Professor Burdon Sanderson, entitled “Photographic Determina¬ 
tion of the Time-relations of the Changes which take place in Muscle during the 
Period of so-called ‘ Latent Stimulation (‘ Boy. Soc. Proc.,’ vol. 48, p. 14), it was 
stated that in the gastrocnemius of the Frog the electrical response to an instantaneous 
stimulus, as investigated with the aid of the capillary electrometer, is indicated by a 
sudden movement of the mercurial column of very short duration, and that the photo¬ 
graphic expression of that movement shows that between the contacts two electrical 
changes of opposite sign, and not more than one two-hundredth of a second in 
duration, have immediately followed each other, or, more explicitly, that the spot 
excited became for about 0‘005 sec. first negative, then for a similar period positive, 
to the other contact. 
This statement relates exclusively to the case in which the effect is led off to the 
electrometer by two electrodes of which one ( f) is placed on the tendon, and the 
other (m) is on the belly of the muscle. In this case, the photographic record of the 
electrical response to a single excitation of the nerve, resembles the record obtained, 
when in a circuit of the same resistance as the muscle, two currents of the same 
duration follow one another in opposite directions. 
This resemblance between the two cases is, however, only general, for whereas in 
the artificial effect the difference of potential between the two terminals of the electro¬ 
meter remains the same during each phase, changing sign at the moment that the 
first is followed by the second, the difference of potential between the Two spots to 
* [This notch has not been reproduced in the figure. It can easily be seen in the negative even 
without a lens. March 3, 1892. G. J. B.] 
