284 PEACTICAL PHYSIOLOGY 



is attached. As a matter of fact, of these three structures muscle, owing 

 to its increased extensibility during contraction, is the least often 

 ruptured. In order to demonstrate this properly the muscle-prepara- 

 tion is attached to the clamp and lever, as in the last experiment. 

 Arrange the apparatus for stimulating the muscle directly with single 



FIG. 168. Elasticity curve of rubber tubing. The figures represent weights in grms. (M.S.P.) 



maximal induction-shocks, using a spring-key in the primary circuit. 

 Bring the writing point on to a stationary drum and, with the muscle 

 weighted only by the lever, describe an abscissa line corresponding to 

 the resting muscle. With the writing point again at the beginning of 

 this line, stimulate the muscle once and, from the top of the ordinate so 

 marked, draw another abscissa line corresponding to the muscle when 

 contracted. Rotate the drum by hand, so that the writing point is 

 now 5 mm. along the ' resting ' abscissa line ; hang 20 grms. on to 

 the lever and stimulate, so as to record a second ordinate 5 mm. from 

 the first. Repeat this process, increasing the weight by an equal 

 amount each time. In this way Fig. 169 was produced. It is clear 

 that the distance of the lowest point of each ordinate below the 

 'resting' abscissa line represents the extension of the resting muscle 

 by a given weight, and that the distance of the top of the same ordinate 

 below the * contracted ' abscissa line represents the extension, by the same 

 weight, of the muscle when contracted. If the lowest and then the 

 highest points of the ordinate are joined, two curved lines are produced 

 which represent respectively the curves of extension of resting and 

 contracted muscle (Fig. 169). It will be seen that the extensibility of 

 contracted muscle is absolutely greater, and increases more rapidly, 

 than that of resting muscle. Hence, if the observations were carried 



