48 



PHYSIOLOGY 



CHAP. 



Morselli added a contrivance for air- transmission, which made 

 it possible to record the compression of the spring upon a revolving, 

 cylinder, and which transformed the dynamometer into a dynamo- 

 graph, by which the tracing of a series of maximal voluntary 

 contractions of the flexor muscles of the hand, at regular intervals 

 measured by the beats of a metronome, can be recorded. Such 



PIG. 28. Tracing from Waller's dynamograph, to show effects of fatigue and recovery. 



curves show not only the comparative force of the muscles, but 

 also their resistance, or the ease with which they become fatigued. 

 tXlStill more simple is Waller's dynamograph (Fig. 27), in which 

 the pull of the hand upon a strong steel spring is registered 

 directly by a long lever. Fig. 28 shows the tracing of six groups 

 of maximal contractions, at regular intervals ; between each group 



4 there is a uniform pause for rest. The drop in the 



line uniting the apices in each group shows the 

 fatigue of the muscle; the return to the original 

 executed height in the next group represents its 

 recovery during rest. 



The dynamographs of Morselli and Waller are 

 based on the isometric method, and consequently record the maxi- 

 mal tensions of the flexors of the hand, and the correlative internal 

 work; Mosso's ergograph (Fig. 29) is an instrument based on the 

 isotonic method, and it records the maximal contraction of the 



