THE PHYSIOLOGY OF MUSCLE 491 



trical motor. Load gastrocnemius with 50 gm. Use the maximum speed 

 of the drum. As thus arranged, when the key is closed each rotation of 

 the drum will stimulate the muscle and the myograms will be super- 

 imposed, thus allowing of direct comparison of the succeeding curves 

 as the muscle becomes gradually fatigued. Keep up the experiment 

 (with the kymograph always well wound) until the curves are nearly 

 flat. Note in your books the characteristic shape of the myograph at 

 first, midway, and at the last, and also the changes in the different parts 

 of the myogram. If only every tenth contraction is recorded the curves 

 will be more easily discriminated. 



The phenomena of fatigue in muscle are of great importance, for it is 

 by muscular contraction that events are accomplished in animal life, 

 whether it be the signing of a name, the starting of a machine, or the 

 composition of a symphony. By thus superimposing the curves fatigue- 

 differences are strongly brought out as follows : 



At first the curves (the degree of contraction) increase slightly in height 

 as the muscle gets into its best working order. Then they get gradually 

 flatter, and at length are little more than straight lines. The chief 

 characteristic of the fatigued condition of muscle is a slowing in the 

 processes making up the total complex curve. The latent period 

 increases much, from 0.006 second to 0.3 second or so. The contraction- 

 time increases somewhat, but the most marked change is in the length- 

 ening of the relaxation-time. This is increased many times, and when 

 so increased the condition is sometimes called "contractur." After four 

 or five thousand contractions this slowness of relaxation gradually 

 decreases, but never disappears so that the muscle relaxes as quickly 

 as when unfatigued. 



Heat markedly hastens the onset of fatigue, as also does an abnormally 

 large load. White muscle (in the rabbit, etc.) is more easily fatigued 

 than red muscle, and similarly, a supply of blood through the muscle 

 retards fatigue. Recovery takes place rapidly during rest. 



Expt. 49. Muscular Tone. (Apparatus: Stand-rod, femur-clamp, 

 ether, frog.) Lightly etherize the frog and fasten him belly down on 

 the frog-board. Gently open the lower part of the back and divide the 

 roots of the exposed sciatic on one side. Hang up the frog evenly by 

 the lower jaw in the femur-clamp. 



On careful observation from directly in front of the frog, the leg whose 

 motor, sensory, and trophic nerve has been cut will be seen to hang 

 lower and to be more limp than the normal leg. The tone of the muscles 

 being lost, gravity draws down the foot farther than the other. 



Expt. 50. Action-current. (Apparatus: Two nerve-muscle prepara- 

 tions with long nerves, frog's heart.) This experiment has long been 

 known as the "rheoscopic (current-showing) frog." (A) On the gastroc- 

 nemius. With the two muscles on the glass plate, lay the nerve of 

 muscle No. 1 longitudinally over muscle No. 2. Stimulate the central 

 end of the nerve of muscle No. 2 with make shocks from one cell, using 

 the platinum electrode for the purpose. If the nerve be properly arranged 



