LABORATORY MANUAL OF PHYSIOLOGY 



For recording the contractions of human voluntary muscle, either 

 the ergograph of Mosso or that of Porter may be used. With the 

 former, the flexion of the middle finger is recorded ; with the latter 

 the contractions of the abductor indicis. 



1 . If the Mosso instrument is used, place the forearm and fingers 

 in the securing attachments of the apparatus and weight the mid- 

 dle finger with one or two kilograms. Contract the muscles, vol- 

 untarily, once every two seconds, keeping time to the beat of a 

 metronome, until you are no longer able to bring about a contrac- 

 tion in this way. The contractions should be recorded upon a 

 slowly revolving drum. Now stimulate the flexor muscles directly 

 with electrodes placed over the forearm, using the same frequency 

 of stimulation as before, one every two seconds. Does the muscle 

 respond to direct stimulation after fatigue has been induced to vo- 

 litional impulses ? 



2. Repeat with a new subject, reversing the procedure. In 

 other words, stimulate the muscle artificially until it no longer re- 

 sponds and then attempt to flex the finger voluntarily until com- 

 plete fatigue is obtained. 



3. With a fresh subject, induce voluntary fatigue and record the 

 time. Allow the muscles to rest for five minutes and repeat voli- 

 tional contractions until fatigue has again occurred. How does the 

 time of fatigue onset, after the rest, compare with that of the first 

 series of contractions ? 



4. Now, instead of mere rest, give the forearm five minutes' mas- 

 sage and repeat the ergograph experiment. Is the onset of fatigue 

 delayed as compared with the first series of contractions, or with 

 the second, or with both ? What is the effect of massage ? 



XIX. INFLUENCE OF TENSION ON THE MUSCLE CONTRAC- 

 TION. ISOMETRIC CONTRACTION. 



In the preceding experiments, the resistance offered to the muscle 

 during its contraction, as measured by the weight lifted, has been 

 nearly uniform, of course excepting the inertia of the weight at the 

 beginning of the lift. A muscle twitch under these circumstances 



[33] 



