1883.] Variations of Latency in certain Skeletal Muscles. 289 



obtained where the muscle is transfixed by the lever. An intra-latent 

 lengthening of the entire muscle does occasionally occur, but in our 

 experiments it had no constant relationship whatever to the time of 

 stimulation, and we therefore regarded it as a chance extension. "We 

 have not, however, been able to find time to repeat the experiments — 

 using his methods — from which Gad deduces his results. 



The brief latency that Place and Klunder obtained from stimulation 

 of the already shortening muscle, we have rarely seen. When it does 

 occur, its accurate estimation becomes extremely difficult, as it is 

 necessary to separate the moment when active contraction commences 

 from the passive shortening which preceded it, and one phase often 

 passes into the other by almost insensible gradations. Fallacies of so 

 extensive a nature arise from the use of a slowly moving recording 

 surface, and of a short lever, that we have in all cases employed a 

 rapid swing of the pendulum myograph, and a lever multiplying the 

 contraction by six or seven times, for the production of the curves from 

 which our data of latencies are taken. In the fatigued muscle, 

 for instance, commencing contraction is very gradual ; so gradual in 

 fact that its earlier phases may, with a short lever, be readily mistaken 

 for a prolongation of the latency. We need not point out that with a 

 comparatively slowly moving cylinder slight inaccuracies in measure- 

 ment — at all times subject to occur — are multiplied proportionally as 

 the speed becomes slower. 



A cursory examination of the tables in our first communication 

 shows that of the causes therein examined, the most potent in affect- 

 ing the latency are variations in temperature and fatigue ; of 

 secondary importance are the strength of stimulation and the mode 

 of suspension of the extending weight. 



Temperature. — In the gastrocnemius of an " April frog " (indirect 

 stimulation) we saw for an excursion through 20° C. (viz., from 5° to 

 25°) a variation of -014" in the length of the latency ; in the muscle 

 of another animal heated from the normal room temperature (17°) 

 through 14° C, a variation of *01" was obtained. Taking the room 

 temperature as the starting point, we find in these experiments that 

 lowering the temperature through 5° increased the latency , 004 // , 

 •0033", and *0027" respectively. Heating* through 5° above the 

 normal yielded a shortening of -0016" — "0012", but though these 

 figures represent a usual result, occasionally there is a much more 

 extensive variation. Thus, in one case with an unusually long 

 latency ('01 7") at the room temperature, heating through 5° reduced 

 the latency '01". After this point in the heating process had been 

 reached, the course of the latency under higher temperatures was 

 strictly comparable with that of other muscles with a more ordinary 

 initial latency, and we should regard this circumstance as furnishing 

 a proof that this abnormally long latency was in reality owing to 



vol. xxxv. u 



