366 LAWS OF MUSCULAR CONTRACTION. 



The rapidity of Sdcretnn's second axis is hardly sufficient 

 to bring out the latent period with sufficient distinctness; but 

 the other characters of the curve may be very well shown. 



The third, swiftest, axis may be used, but there are diffi- 

 culties in managing it. Care must be taken to reduce the 

 friction of the various recording points to a minimum ; and 

 the observation should not be taken till towards the end of 

 the second revolution. Before that, the cylinder is far from 

 reaching its maximum (uniform) speed; after that, the over- 

 lapping curves of the tuning-fork are difficult to decipher. 



1 Setter results are obtained if the cylinder be used horizon- 

 tall}" (the natural position of the apparatus) instead of verti- 

 cally. The lever tuning-fork and marking key will of course 

 have to be arranged accordingly. 



"When the heavier myographion lever is emplo} r ed, the effect 

 of the inertia of the lever will make itself manifest in a secon- 

 dary curve, at the end of the muscle curve. 



(For more exact observations than are furnished by Fon- 

 cault's second axis, it is better to employ the pendulum myo- 

 J//V//////OH, see, Wundt Mechanik der Nerveu, p. G.) 



A muscular contraction, even when produced by an instan- 

 taneous electric shock, takes a measurable time for its com- 

 plete development. The contraction does not begin at the 

 moment when the stimulus breaks into the muscle, but is pre- 

 ceded by a latent period. The contraction curve rises at first 

 very rapidly, but afterwards more slowly, and having reached 

 a maximum, declines at first slowly, afterwards more rapidly, 

 and lastly more slowly again. 



The advanced student may determine by the same method 

 the variations in the character of the muscle curve, caused 

 by : 



1. Exhaustion. Ob$. II. Having determined with a single 

 induction shock the natural curve, exhaust the muscle by pro- 

 longed or repeated stimulation with the interrupted current, 

 and then repeat again with the same single induction shock as 

 before. The curve will be not only of less height, but will be 

 longer, />., the contraction will be slower, and the latent period 

 especially will be prolonged. 



2. Heat and Oold.-~0fo. III. The temperature of the 

 chamber may be raised or lowered by introducing a current 

 of moist hot air or pieces of ice into it. 



It is more convenient, however, to use the frog in a hori- 

 zontal position, simply laying bare the gastrocnemius, and 

 dividing its tendon (see Chap. XIX., sec. XL), and then 

 placing tha muscle in a double trough, made by bending a 

 pu < < of leaden tube. Having determined the natural curve, 

 pass hot or ice-cold water through the tube, and determine the 

 curve at various temperatures. 



