48 



PRACTICAL PHYSIOLOGY 



The trace upon the drum must not be looked at during the 

 experiment. 



(Read Simple Muscular Contraction and factors modifying it 

 in Text Book.) 



Lesson X. Apparatus as in last lesson. 



1. Series of weights to attach to lever 5-10-20-30 gms. 2. Normal saline. 

 3. Broken ice. 



To be provided for Class. 

 Mosso's or Porter's Ergograph. 



LESSON XI 



6. The Effect of a Rapid Succession of Stimuli. 



METHODS.!. With a fast drum, arrange the two strikers on the 

 axle, well apart from one another, and, with breaking shocks, take 

 a trace of two muscle twitches near the bottom of the drum. Mark 

 the moments of stimulation. Then approximate the strikers so 

 that the second contraction will be produced before the first has 



FIG. 45. Arrangement for investigating the Effect of a Rapid Succession 



of Stimuli. 



1. Induction Coil. 



2. Drum. 



3. Frog-board. 



4. Mercury Key. 



5. Friction Key. 



6. Vibrating Spring with Cup containing Mercury. 



7. Gear for producing Slow Rotation of the Drum. 



ceased, move the drum so that the lever writes at a higher level, 

 and take a trace. 



Note the relationship of the second contraction to the first, 

 upon which it is superimposed. Mark the moments of stimulation, 

 and take a time trace. 



2. Now disconnect the drum from the primary circuit and 

 introduce a spring (Fig. 45 and Appendix or as in Fig. 47). Adjust 

 the current to stimulate on breaking. (1) Set the drum going 

 slowly (slow gear large spindle to small), and set the spring so that 

 it makes and breaks three to five times per second (timing with 

 your watch), and note its length. The arrangement shown in Fig. 

 47 may be used. Bring the point of the lever upon the drum. 

 Start the spring vibrating. Open the key in the secondary circuit 



