464 



Drs. G. F. Yeo and T. Cash. 



The instrument which served us for registration of the contraction 

 was a modification of Fick's pendulum myograph, manufactured by 

 the Cambridge Scientific Instrument Company. It was provided with 

 an extensive arc, having movable catch adjustments, so that the 

 velocity of the recording surface could be readily modified. The 

 primary current was broken by the arm of the swinging |Dendulum, 

 and if occasion required a second contact, the relation of which to its 

 neighbour could be regulated by a micrometer screw, could be em- 

 ployed in conjunction. The recording plate could be elevated so as to 

 register a series of some 30 — 40 curves, one over the other. The moist 

 chamber, containing the muscle, &c, was placed on a table which 

 could be withdrawn or advanced to meet the plate (acting like the 

 slide-rest of a lathe) without altering the relationship of the writing 

 point to the recording surface. Within the moist chamber, and sur- 

 rounding the muscle, passed several coils of metal tubing, which could 

 be heated or cooled at pleasure by passing heated or iced water through 

 it from a system of tubes terminating above in double funnels. 



The temperature was accurately measured by a Centigrade thermo- 

 meter placed in the moist chamber, its bulb being equidistant from the 

 muscle and the tubing. The lever, designed by one of us, was made 

 of two straws separated to the extent of 1-J inch at their union with 

 the axis, and converging at the other end to a pointed strip of pla- 

 tinum foil, which acted as a pen. The weight of this lever, without 

 the friction of the pen, was about 1 grm. The weight was suspended 

 round the axis of rotation, except in those cases in which it appeared 

 desirable to apply it in the line of traction of the muscle. Great 

 steadiness, absence of appreciable friction, and elimination of the effect 

 of the " throw up " sustained by a lever weighted anywhere except at 

 its axis, were ensured by this adjustment, and the great lightness of 

 the lever arm. 



In view of the fact that the nerve is more rapidly influenced by 

 those agents which we proposed to employ in modifying the manifes- 

 tations of latency, and also because we desired to look chiefly to the 

 actual effect such agents produced on the changes necessary to the 

 subsequent contraction, rather than to the varying conductivities of 

 the nerve, we chose the curarised muscles (the gastrocnemius of the 

 frog) for the bulk of our experiments. We may mention in this 

 place that we found the variations between the non-curarised and 

 curarised muscles, both stimulated directly and at room temperature 

 (17 — 18° C), so slight that they may be disregarded. 



Maximal stimulation was employed in all cases, except where other- 

 wise specified. Our experiments were performed on Bana tenvp., 

 between the 10th January and the middle of April. 



Though we have thought well to give frequently the measurement 

 of a series of curves taken from a single muscle, we have done this 



