96 



PHYSIOLOGY OF MUSCLE AND NERVE 



as 6.25 kilograms, a value which is considerably higher than the pre- 

 ceding one for frog's muscle. This calculation becomes of practical 

 value in testing the power of the muscles of persons suffering from 

 various types of nervous diseases. A so-called dynamograph is com- 

 monly used for these determinations. This instrument consists of a 

 tension-spring against which the muscles of the hand are voluntarily 

 contracted. 



A close study of the curve represented by Fig. 43 also shows that a 

 muscle reacts better when a slight load is attached to it than when it is 

 not weighted at all. To begin with, therefore, the contractions in- 

 crease in height, quickly at first and then more slowly, until a certain 



Fig. 52. — Diagram op Work-adder. 

 A, wheel which is turned by muscle M in direction of arrows. It is held in place 

 by brake B. Each contraction of muscle raises weight W . 



maximum has been reached. 'Subsequent to this point the increasing 

 loads gradually diminish the contractions until the muscle is no longer 

 able to raise the lever above the abscissa. Hence, a muscle yields 

 maximal work only when made to act against a certain moderate 

 weight which places it under a physiological tension. 



In order to determine the work performed by a muscle during a long 

 period of time, it becomes necessary at times to employ an ergograph 

 or a work-adder.* The former instrument has been described in an 

 earlier chapter. The latter consists of a small windlass which the 

 muscle (Af ) turns sUghtly in one direction with each contraction. The 

 weight (TF) which is suspended from the wheel (^) by a thread is 

 * Fick, Unters. aus dem physiol. Lab. der Zuricher Hochschule, Wien, 1869. 



