34 



.\DVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



may be kept in the horizontal position without putting an additional 

 weight upon the resting muscle. 



Stimulate the muscle successively with the make and break shocks 

 of a constant current, moving the drum each time by hand a distance 

 of a few millimeters. Repeat with single induction shocks of medium 

 strength. Allow the drum to revolve first slowly and then more rapidly, 

 and repeat the stimulations. Obtain intermediate speeds of the drum 

 by placing fans of different size upon the pivot of the starting gear. 

 Observe the changes in the out- 

 line of the myogram as the speed 

 is increased. 



Fasten a tuning-fork, vibrat- 

 ing one hundred times in a second, 

 to a separate stand/ and allow its 

 beats to be registered below- the 

 myogram. 



Stimulate the muscle with a 

 quickly interrupted current (posts 

 1 and 3) for a period of five 

 seconds, and record its contrac- 

 tion upon a slowly revolving 

 drum. Never permit the tracing 

 to extend across the line where 

 the paper has been glued together. 



10. Fixation of the Records. Write your name upon the paper and 

 label the different tracings. Remove the drum from the stand, and 

 hold it in your left hand with the tip of the thumb upon the edge of the 

 paper. Insert the tip of a small forceps underneath the paper near 

 the line where its ends have been glued together. Break the paper 

 in a straight line. Hold the paper firmly between your hands and 

 draw it with the blackened surface turned upward through a solution 

 of shellac in alcohol. Suspend the paper in the frame provided for this 

 purpose and allow it to dry. Cut out the different tracings and paste 

 them in your note-book in an orderly manner. 



11. Isotonic and Isometric Myograms. If a muscle is made to con- 

 tract against a writing lever and a slight load, a very small portion of 

 its energy will be used up in overcoming this resistance. By far the 

 greatest amount of its energy, however, will be set free to yield visible 

 mechanical energy, heat, and a small fraction of electricity. If the 

 muscle is now attached near the fulcrum of the lever, while the end near 

 the writing point is prevented from moving by a counter-force, the 

 shortening of its fibers will be reduced to a minimum and practically no 

 mechanical energy will be liberated. A relatively much larger amount 

 of the total energy will thereby be converted into heat. The former 

 arrangement is characterized as isotonic and the latter as isometric. 



FIG. 12. ARRANGEMENT FOR SMOKING THE 

 PAPER. (Univ. of Penna. Lab. Outlines.) 



