88 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Bernstein 1 measured the rate at which the irritating process is transmitted 

 along the muscle by recording the latent period, the time elapsing between the 



Fin. 34.— Method of recording the rate of passage of the contraction process along a muscle (after 

 Marey). The movements of the muscle are recorded by means of air-transmission. The pince myo- 

 graphique consists of two light bars, the upper of which acts as a lever, moving freely on an axis sup- 

 ported by the lower. When the free end of the upper bar is raised, the other end presses down on a 

 delicate rubber membrane which covers a little metal capsule, which is carried on the corresponding 

 extremity of the Lower bar. The capsule is in air-communication, by a stiff-walled rubber tube, with 

 another capsule which is similarly covered with rubber membrane. A light lever is connected with the 

 membrane of the second tambour, and records its movements on the surface of a revolving cylinder. 

 The muscle is placed between the free ends of the bars of the pince myographique, and, when the muscle 

 thickens in contraction, it raises one end of the lever, depresses the membrane at the other end, and 

 drives air into the recording tambour, and thus, by automatically raising the writing-point, records its 

 change in form on the cylinder. 



moment of irritation and the beginning of the contraction (see p. 102). A 

 lever was so connected with one end of the muscle as to record the instant that 

 it began to thicken. The muscle was stimulated in one experiment at the end 

 from which the record of its contraction was taken, and in another immediately 

 following experiment it was stimulated near the other end. The distance 

 between the stimulated points being known, the rate of transmission was 

 reckoned from the difference in the latent periods. In his experiments he 

 found the rate of conduction in the semimembranosus of the frog to be from 

 3.2 to 4.4 meters per second. Hermann found the rate to be 2.7 meters for 

 the curarized sartorius of the frog. The results obtained by Abey and some 

 others are a little lower, but probably 3 meters per second can be accepted as 

 the average normal rate for frog's muscle. 



Length of Wave. — By such experiments it becomes obvious that the con- 

 traction process passes over the muscle, in the form of a wave. In an experi- 

 ment, such as Bernstein's, in which the thickening of the muscle is recorded, 

 we can determine from the length of the curve written by the contracting 

 muscle how long the contraction remains at a given place. Knowing this, 

 and the rate at which the pine— passes along the fibre, we can estimate the 

 length of the contraction wave, just as we could reckon the length of a train 



1 Untersuchunyen iiber die elektrische Errerjung von Muskeln unci Nerven, 1871, S. 79. 



