THE PHYSIOLOGY OF MUSCLE 495 



the muscle is loaded with a scale-pan only. Turn the drum (by hand) 

 1 mm. Add 1 gm. to the scale-pan and stimulate exactly as before. 

 Continue thus, adding a gram each time until the load is 10 gm. Then 

 add 5 gm. before each stimulation and record, and continue until the 

 muscle no longer contracts (1000 grams?). Observe (a) the increase 

 in the contraction's height by a moderate load, and (6) the decrease as 

 the loads are further increased. (Figure out the power-index of the 

 muscle, keeping its bipenniform shape in mind.) 



This is further evidence of the important principle that a muscle works 

 best under normal conditions. The average resistance to contraction 

 is one of these conditions, here represented by weights. When a muscle 

 attempts to contract against a weight which it cannot at all lift, it is 

 obvious that the muscle is expending much energy, as, indeed, might be 

 easily demonstrated by calorimetric measurements of the heat, water, 

 carbon dioxide, and nitrogen excreted and of the oxygen and food con- 

 sumed. Hence in the biological definition of work the space and move- 

 ments involved are of a minute or even molecular nature. 



Expt. 55. Volume of Contracting Muscles Does Not Increase. 

 (Apparatus : Volume-tube, stand-rod, etc., inductorium, modified Ringer's 

 solution, entire leg of frog.) Place the frog's leg in the tube and hook 

 the lower electrode into one end of it. Fill the tube quite full of the 

 Ringer's fluid, insert the rubber stopper and hook the upper electrode 

 into the upper end of the mass of muscles, being careful that no bubbles 

 of air whatever remain in the tube. Push down the plunger-rod until 

 the solution rises well into the capillary. Now pass a maximal alter- 

 nating induction-current through the leg, making it contract and continue 

 contracted. The liquid does not rise in the capillary tube, proving that 

 the volume does not increase while the shape changes. Does the volume 

 decrease ? 



During the contraction of cross-striated muscle (Schafer) the sarcoplasm 

 of each sarcomere passes into the longitudinal canals of the latter, being 

 stopped by the transverse Krause's membrane in the middle of each 

 sarcomere. Thus the fibril is thickened and shortened, doing its part 

 in this way to shorten the whole muscle and so to approximate its ends. 



Expt. 56. Effects of Heat and of Cold on Contraction. (Apparatus: 

 Muscle-cooler-and-heater, myograph, inductorium, finely cracked ice, 

 salt, Bunsen burner.) Place the cooler-and-heater on a stand-rod high 

 enough so that the lamp or burner will stand far beneath the side tube. 

 Make a gastrocnemius muscle preparation, place the femur in the screw- 

 clamp inside the cover of the cooler, having attached a fine copper wire to 

 the tendo Achillis. Pass the end of this wire through the hole in the bottom 

 of the collar and attach it to the muscle-lever in the usual way, arranged 

 to write on the smoked drum. Fill the space around the muscle-cham- 

 ber solid full with finely cracked ice and sprinkle on a few grams of salt 

 before covering. When the temperature has reached a degree or two 

 above zero, stimulate the muscle with a single maximal break induction 

 shock and record an accompanying time line. Have the drum rotate at 



