THE PHYSIOLOGY OF MUSCLE 497 



lessened, the time of 55 being approximately half that at 5. (4) In- 

 crease of temperature lessens the relaxation-period of the muscle, that 

 at 30 being from 25 to 15 per cent, that at 5. These estimates are for 

 the gastrocnemius of the frog, and apply in detail to no other muscle, 

 and even here are not at all constant. 



Expt. 57. Work Done by a Muscle. (Apparatus: Work-adder, 

 inductorium, kymograph, centimeter-rule.) Arrange the gastrocnemius 

 muscle above the work-adder so that the lever of the latter will write on 

 the drum, while the thread with 50 gm. on its end hangs over the edge 

 of the table, the weight nearly on the floor. Mark with ink the spot on 

 the thread at the top of the base of the work-adder. Now stimulate the 

 muscle with single maximal break induction-shocks (carefully cutting 

 out makes as usual) every three seconds by the watch. Continue this 

 until the muscle no longer moves the lever or winds up the thread. 

 Have the drum rotate slowly so that the myograms shall be very close 

 together and all on one line around the drum. Mark with ink the thread 

 (at the same level as before) at the end of the muscle's work. Unwind 

 the thread from the wheel and measure the distance in centimeters 

 between the ink-marks. This number multiplied by fifty (grams of 

 weight lifted) gives the gram-centimeters of work the particular muscle 

 did under the conditions of the experiment. Note the changing height 

 of the myograms, and the shape of the curve connecting their summits. 



The energy of muscle is derived from the chemical katabolism of 

 carbohydrates (largely glycogen), fats, and proteids. In man about a 

 third may be given out as muscular work. Fick found that of the latent 

 energy in a muscle resisted by a heavy load, one-third may be used to 

 lift this load, while, if the latter be light, not over 5 per cent, is utilized 

 mechanically, the muscle then working at a disadvantage. 



A heavily loaded muscle, then, does more work than one lightly loaded. 

 With 70 gm. load the work done may be nearly ten times as great as when 

 the load was 5 gm., while the length of the lift may be much less. The 

 muscles of homotherms are stronger than those of poikilotherms, but the 

 muscles of insects are stronger than others and much more active besides. 



Expt. 58. The Contraction-wave. (Apparatus: Two muscle-levers, 

 two stand-rods, cork clamp, femur-clamp, inductorium, kymograph, 

 tuning-fork, millimeter-rule). Place the cork clamp horizontally in the 

 femur-clamp ; arrange the muscle-levers, one on each stand-rod, so that 

 the cork stilts (previously tied on under the levers) may rest on either 

 side of the muscle on the glass plate of the cork clamp, and both write on 

 the drum. It is essential that a line connecting the writing-points of the 

 levers should be exactly vertical, else measurement of the speed of the 

 waves cannot easily be made. 



Now prepare a long narrow strip of muscle, including the sartorius, 

 from the thigh of the frog, and place it under the cork clamp (which 

 should be pressed down somewhat lightly) and under the cork stilts of 

 the levers. When the drum is rotating at its maximum speed, stimulate 

 one end of the muscle with one maximal break induction-shock (the 

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