222 Buchanan 



the form of a compressible steel ellipse with scale. That electrode which 

 was over the part of the muscle felt to become most tense when the 

 dynamometer was squeezed was, to begin with, always connected with the 

 acid of the electrometer. The image of the meniscus was projected through 

 a slit on to a photographic plate moving at a known and equable rate 

 inside a dark box. There being no eye-piece to the microscope, the image 

 was inverted. The distance of the plate from the image was such as to 

 magnify it with the objective used about three hundred times in all cases. 

 The late of movement of the plate was shown by the vibrations of a spring 

 in unison with, and driven by, a 100 tuning fork. The trolley carrying 

 the photographic plate broke a key when it began to pass the slit which 

 left a record on the plate of the moment at which it was broken. The 

 subject was, as a rule, told to contract the muscle that was being investigated 

 — to clench his tist or his jaws, for instance — only when he heard this key 

 break, so that while he was reacting to sound the meniscus might inscribe 

 its resting position on the plate. 



The effect observed. Evidence tluit it is not to be attributed 

 to inequalities of pressure of the skin on the electrodes. — Fig. 4 

 is typical of the effect produced upon the electrometer by the flexores 

 digitorum. After recording it for the first time, I made the following 

 experiment for the purpose of ascertaining whether or not what I had re- 

 corded could be due to variations in the pressure of the skin against the 

 sponge, for such variations there must undoubtedly be when the muscle 

 suddenly becomes tense. A piece of dry bandage was tied loosely round 

 the arm of the subject, electrode and all, at the place where the tension of 

 the muscle becomes greatest when the fist is clenched. A second person, 

 holding the ends of the bandage, pulled them as hard as he could, so as to 

 tightly press the zinc rod and intervening sponge against the arm of the 

 subject while the plate was passing the slit, the subject himself being passive. 

 The plate was passed through under such conditions alternately with other 

 plates which were passed through while the subject was actively- clenching 

 his fist, beginning to do so at the sound of the signal. While all 

 photographs taken with the muscle contracting at the given signal showed 

 an effect of the kind reproduced in fig. 4, all those taken with the muscle 

 passive, but the pressure on the skin increased by the second person, 

 showed a meniscus tracing as smooth throughout as that seen during the 

 reaction time in the alternate photographs. This experiment makes the 

 presumption strong that the effect observed when the muscle contracts 

 actively is really a muscular effect. 



What strikes us most in all the records is the great irregularity of the 

 undulations which indicate electrical variations, irregularity both in duration 

 and in the steepness which in capillary electrometer records indicates 

 amount, or strength, of variation. The irregularity is of the same kind 

 and the variations have the same sort of frequency as have the wavelets 

 in records obtained with many frog's muscles in strychnine spasm 



