22 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



extensions by the height of the ordinates dropped from each 

 point. If the ends of the ordinates are joined, the result is a 

 straight Hne. When a similar experiment is made with a living 

 muscle it is found that the extension is not proportional to the 

 weight used. The amount of extension is greatest in the begin- 

 ning and decreases proportionately with new increments of 

 weight. If the results of such an experiment are plotted, as 

 above, representing the equal increments of weight by equal 

 distances along the abscissa and the resulting extensions by ordi- 

 nates dropped from these points, then upon joining the ends of 

 the ordinates we obtain a curve concave to the abscissa. At 

 first the muscle shows a relatively large extension, but the effect 

 becomes less and less with each new increment of weight, the 

 curve at the end approaching slowly to a horizontal. If the 

 weight is increased until it is sufficient to overcome the elasticity 

 of the muscle the curve is altered — it 

 becomes convex to the abscissa, or, in 

 other words, the amount of extension 

 increases with increasing increments of 

 weight up to the point of rupture, as 

 shown in the accompanying curve* 

 (Fig. 5). It should be added also that 

 the amount of deformation exhibited 

 by a muscle or other living tissue placed 

 under a stress varies with the time that 

 the stress is allowed to act. The 

 muscle is composed of viscous material, 

 and yields slowly to the force acting 

 upon it. In experiments of this kind, 

 therefore, the weights should be al- 

 lowed to act for equal intervals of time. 

 It has been shown that the extensibihty 

 of a muscle is greater in the contracted 

 than in the resting state. 



The curve of extension described 

 above for skeletal muscle holds also for 

 so-called plain muscle. This latter 

 tissue forms a portion of the walls of the 

 various viscera, the stomach, bladder, 

 uterus, blood-vessels, etc., and the facts 

 shown by the above curve enter fre- 

 quently into the explanation of the phys- 

 ical phenomena exhibited by the viscera. 

 For instance, it follows from this curve that the force of the heart 

 * See Marey, "Du mouvement dans les fonctions de la vie," 1868, p. 284. 



Fig. 5. — Curve given by 

 Marey to show the effect upon 

 the extension of muscle caused 

 by increasing the load regularly 

 to the point of rupture: From 

 o to a the extension of the 

 muscle decreases as the weight 

 increases, giving a curve concave 

 to the abscissa; at a the Hmit 

 of elasticity is passed and the 

 muscle lengthens by increasing 

 extensions for equal increments; 

 at X rupture (750 gms. for frog's 

 gastrocnemius) . 



