BY DR. MICHAEL FOSTER. 365 



CHAPTER XXII. 

 PHENOMENA AND LAWS OF MUSCULAR CONTRACTION. 



I. The Muscle Curve. In order to study the muscle 

 curve, the recording surface must travel with sufficient 

 rapidity. (The chief features of the curve may be seen when 

 Secretan's cylinder with Foucault's regulator revolves on the 

 second axis.) 



06s. I. Arrange a muscle preparation in the moist chamber. 

 The electrodes should be placed at some little distance from 

 each other on the muscle itself; the nerve consequently need 

 not be prepared. Load with 10 or 15 grms. Underneath the 

 point of the lever bring the recording tuning-fork to bear on 

 the cylinder. 



Arrange for a single opening induction shock, but instead 

 of the key b (Chap. XIX., sec. XIII.), insert the marking key, 

 simply introducing it into one wire from the battery, so that 

 when the lever is down the current passes, but when it is 

 raised (and the point depressed) the current is broken (Chap. 

 XIX., sec. X.). The point of the marking key must be 

 brought close under the recording point of the lever but 

 above the recording point of the tuning-fork. Place all three 

 recording points very carefully in the same vertical line. 



The marking key being closed, and the tuning-fork vibrat- 

 ing, open the key a, and remove the break from the governor 

 of the clock-work , when the cylinder is approaching the end 

 of the first revolution, open the marking key, and as soon as 

 possible afterwards stop the cylinder. 



On the cylinder there will now be seen three lines of mark- 

 ing (see fig. 279) ; a is the line of the marking key, and the 

 point where it descends indicates the moment at which the 

 current broke into the muscle ; b is the line of the tuning-fork, 

 and each complete curve denotes a certain fraction of a second 

 (determined by the pitch of the tuning-fork) ; c is the line of 

 the muscle-lever, m 1 marks the moment of the beginning of 

 the contraction, m? the curve's highest point, m 3 its termina- 

 tion. Draw a straight vertical line m through the point where 

 the line a descends, and similar vertical (parallel) lines ??i, m 1 , 

 r/i 2 , wi s , cutting a b and c. 



m m 1 will give by measurement off b the duration of the 

 latent period m 1 m*, of the rise; m' 1 ?TI S , of the fall; and m 1 

 ?u s , of the total contraction. 



