52 



ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



upon the index-finger and connecting the latter with the lever is moved far out 

 toward the writing point. Isometric effects result if the vertical rod is adjusted 

 near the metal support of the lever (Fig. 31). 



2. Dynamometer. Place a dynamometer in your right hand and 

 contract the muscles against its spring. How great a force can you 

 exert? Repeat with the left hand. Compare. 



3. Ergographic Record of the Frog's Gastrocnemius. Procure a 

 metronome and insert it in the primary circuit of the induct orium. 

 Adjust it to yield one stimulus in every second. Pith a frog and pre- 

 pare a gastrocnemius muscle. Attach it to the writing lever in the 

 usual manner. Allow the drum of the kymograph to revolve at a slow 

 rate, and register the successive contractions of the muscle until fatigue 



FIG. 31. SPRING ERGOGRAPH. (Harvard Apparatus Co.) 



has set in. How many contractions have been obtained and during 

 how long a period? 



4. The Influence of the Blood-supply Upon Muscular Contraction. 

 Procure a metronome and insert it in the primary circuit of the induc- 

 torium. Adjust this instrument to stimulate once in every second. 

 Pith a frog and block the opening with a pointed piece of match so that 

 no blood is lost. Fasten the frog upon a narrow board of cork raised 

 to the height of the upper margin of the drum of the kymograph. 

 Isolate the femoral blood-vessels on one side and ligate them. Make an 

 incision through the skin of the ankle and separate the tendo achillis 

 from the bone. Attach a silk thread to the tendon and connect it across 

 a pulley wheel with a writing lever adjusted upon the paper of the 

 kymograph underneath the edge of the cork board. Isolate the oppo- 

 site tendo achillis in the same way, and connect it with a second writ- 



