620 A MANUAL OF PHYSIOLOGY 



take off the writing-point, and remove all unmelted ice or snow. 

 With a fine-pointed pipette irrigate the muscle with normal saline at 

 30 C., and quickly take another tracing. Then put on a time- 

 tracing with the electrical tuning-fork. Fig. 171, p. 564, shows a 

 series of curves obtained in this way. 



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

 as in 9. Take a tracing first with the lever alone, then with a weight 

 of 10 grammes, then with 50, 100, 200, and 500 grammes (Fig. 170, 



P- 563)- 



11. Influence of Fatigue on the Muscle-curve. Arrange as in 10, 

 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 

 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. 192). 

 (For specimen curve, see Fig. 175, p. 567.) 



12. Seat of Exhaustion in Fatigue of the Muscle-nerve Prepara- 

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

 preparation has been stimulated until contraction no longer occurs, 

 the muscle can be made to contract by direct stimulation. The seat 

 of exhaustion is, therefore, not the muscular fibres themselves. To 

 determine whether it is the nerve-fibres or the nerve-endings, 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 s?de on the same pair of electrodes. Cover 

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

 secondary of an induction-machine arranged for tetanus. With a 

 camel's-hair brush moisten one of the nerves between the electrodes 

 and the muscle with a mixture of equal parts of ether and alcohol, 

 diluted with twice its volume of water, to abolish the conductivity. 

 Or put the mixture in a small bottle, in which dips a piece of filter- 

 paper. The projecting end of the filter-paper is pointed, and the 

 nerve is laid on the point. As soon as it is possible to stimulate 

 the nerves without obtaining contraction in this muscle, proceed to 

 tetanize both nerves till the contracting muscle is exhausted. If the 

 other muscle begins to twitch during the stimulation, more of the 

 ether mixture must be painted on the nerve. As soon as the stimula- 

 tion ceases to cause contraction in the non-etherized preparation, 

 wash off the mixture from the other nerve with normal saline, and 

 soon contraction may be seen to take place in the muscle of this 

 preparation. This shows that the nerve-trunk is still excitable. 

 Now, both nerves have been equally stimulated, and therefore the 

 exhaustion in the non-etherized preparation was not due to fatigue 

 of the nerve-fibres, but of the nerve-endings. 



(b) Inject | gramme chloral hydrate into the rectum of a rabbit, 



