70S A MANUAL OF PHYSIOLOGY 



Now stop the drum, mark with a pencil the position of the feet of the 

 stand carrying the myograph plate, take the writing-point off the 

 drum, and surround the muscle with pounded ice or snow. After a 

 couple of minutes brush away any ice which could hinder the move- 

 ment of the muscle, rapidly replace the stand in exactly its original 

 position, with the writing-point on the drum, and take another 

 tracing. Again take off the writing-point, and remove all unmelted 

 ice or snow. With a fine-pointed pipette irrigate the muscle with 

 physiological salt solution at 30 C., and quickly take another 

 tracing. Then put on a time -tracing with the electrical tuning- 

 fork. Fig. 233, p. 646, shows a series of curves obtained in this way. 



7. Influence of Load on the Muscle-curve. Arrange everything 

 as in 6. Take a tracing first with the lever alone, then with a weight 

 of 10 grammes, then with 50, 100, 200, and 500 grammes (Fig. 232, 

 p. 646). 



8. Influence of Fatigue on the Muscle-curve. Arrange as in 7, 

 but leave on the same weight (say 10 grammes) all the time. Place 

 the nerve on the electrodes. Leave the short-circuiting key open. 

 The nerve will be stimulated at each revolution of the drum, and the 



FIG. 262. ARRANGEMENT FOR STUDYING VOLUNTARY MUSCULAR FATIGUE. 



writing-point will trace a series of curves, which become lower, and 

 especially longer, as the preparation is fatigued. Two or four 

 curves can be taken at the same time, if both ends of one or of two 

 brass slips be arranged so as to make contact with the projecting 

 wire at an interval of a semicircumference or quadrant of the drum 

 (Fig. 261). (For specimen curve, see Fig. 241, p. 651.) 



9. Seat of Exhaustion in Fatigue of the Muscle-nerve Preparation 

 for Indirect Stimulation. When the nerve of a muscle-nerve prepara- 

 tion has been stimulated until contraction no longer occurs, the 

 muscle can, under ordinary conditions, be made to contract by 

 direct stimulation. The seat of exhaustion is, therefore, not the 

 general contractile substance of the muscular fibres themselves. To 

 determine whether it is the nerve-fibres or some structure or sub- 

 stance intermediate between them and the ordinary contractile 

 substance of the muscle, perform the following experiments : 



(a) Pith a frog ; make two muscle-nerve preparations ; arrange 

 them both on a myograph plate, which has two levers connected 

 with it. Attach each of the muscles to a lever in the usual way, and 

 lay both nerves side by side on the same pair of electrodes. Cover 

 with moist blotting-paper. The electrodes are connected with the 



