222 VETERINARY PHYSIOLOGY 



long it takes to pass between any two points at a known 

 distance from one another. Its velocity is found to vary 

 much according to the kind of muscle and the condition of 

 the muscle. In the frog in good condition it travels at 

 something over three metres per second. When the muscle 

 is in bad condition the wave passes more slowly, and in 

 badly nourished muscle, e.g. in advanced phthisis, it may 

 remain at the point of stimulation {Practical Physiology). 



Contraction of a Muscle as a whole may best be studied 

 under the following heads : — 



\st. The course of contraction. 

 Ind. The extent of contraction. 

 3nZ. The force of contraction. 



Isj^. Course of Contraction (fig. 108). 



By attaching the muscle (ili) to the short limb of a lever 

 {L), (fig. 108), and allowing the point of the lever to mark 

 upon some moving surface, a magnified record of the 

 shortening of the muscle when stimulated may be obtained. 



A revolving cylinder covered with a smoke-blackened 

 glazed paper is frequently used for this purpose, and, to 

 stimulate and mark the moment of stimulation, an induction 



coil (p.c, s.c), with an 

 electro - magnetic marker 

 (T.M.), is introduced in the 

 primary circuit. 



To find the duration of 



-^ -^ g the contraction, a tuning- 



y-'^-^^-^^^^^'^^^^^y'^^^y^^^ fork, vibrating 100 thnes 



Tig. 109. — Trace of Simple Muscle per second, may be made 



Twitch (1) showing periods of lat- . i -i -i, ^• 



, )' ^ <-• ,7 \ J to record its vibration on 



ency (a-b), contraction (h-c), and re- 

 laxation (c-d) ; record of moment of the SUrface (fig. 108, A) 

 stimulation (2) ; and a time record (Practical Physioloqy). 

 made with a tuning-fork vibrating ^ "^ -jo/ 

 100 times per second (3). In this way SUCh a 



tracing as is shown in fig. 



109 is produced. The appearance of the trace will, of course, 



vary with the rate at which the recording surface is moving. 



