14 PHYSIOLOGY CHAP. 



the resistance it encounters during its contraction. Generally 

 speaking, it is said that the weight applied to the muscle impedes 

 contraction while it facilitates relaxation. It is further assumed 

 that a muscle which carries no load i.e. is not influenced by 

 external resistance, as when it floats on mercury shortens with 

 an induced shock, and remains contracted without resuming its 

 initial length. If this were accepted unconditionally it would be 

 in open contradiction with a number of experimental observations, 

 which prove that both contraction and relaxation are active states 

 of the muscle. Kaiser (1900) showed that if the frog's sartorius 

 muscle is carefully dissected out without pulling on it, and dipped 

 in olive oil before being placed on the mercury to minimise friction, 

 it responds to each shock of an induced current by a single 

 diphasic contraction, i.e. after contracting it relaxes at its normal 

 rate. After the first indirect stimulation the muscle regularly 



FIG. 8. Diagram of isotonic myograph. L, lever connected with the muscle at point A, traces the 

 movements with writing-point p on the recording surface. The weight P that pulls on the 

 muscle is fastened by a thread to a little wheel attached to axis a of the lever. 



becomes longer than it was before; but if the stimuli are 

 applied frequently the expansion is less complete a muscle, for 

 instance, 35 mm. long in the initial resting state fails to attain 

 its original length, but becomes successively shorter by 1, 2, or 

 3 mm. 



It may be said in general that the greater the load or the 

 resistance opposed to the contractile phase of muscular activity 

 the less is the shortening and the greater the degree of tension 

 in the muscle, so that shortening and' muscular tension are in 

 inverse ratio. On stimulating a muscle clamped at both ends, 

 the tension can be increased to a maximum without any shortening ; 

 conversely, when a muscle, clamped at one end only and loaded 

 at the other with a small weight, is stimulated, it contracts 

 maximally with the least possible increase of tension. A. Tick 

 (1887) first analysed these two functions of muscular activity, 

 and devised a comparatively simple method by which it was 

 possible to a large extent to eliminate the alterations of tension, 

 while the curve of shortening was simultaneously recorded, or 

 vice versa to minimise the alterations in the length of the muscle 



