two thirds of its length. Then apply to each of the two halves t!m> 

 separated a non-polarizable electrode. Use a galvanic current. 

 Make, and note which limb contracts. After an interval break. 

 \Yhere does contraction start at make and break, respectively? 



b. Cool a curarized muscle by placing on ice covered with paraffin 

 paper (to protect the muscle). \Yhen thoroughly cool place in a 

 Gaskell clamp and bathe with ice cold salt solution. Bring non- 

 polarizable electrodes against the opposite ends of the clamped mu>- 

 cle and stimulate as before. Results ? 



c. Remove the rectus abdominis muscle from a frog, lay on a 

 dry glass or porcelain plate and apply non-polarizable electrodes 

 to either end. Stimulate with the galvanic current and note what 

 occurs (close observation is required here) in the region of the 

 tendinous bands which divide the muscle into segments? Is polar 

 stimulation indicated? The effect is most distinct with a cold muscle. 



188. Does muscle change volume in contraction/ Remove the 

 skin from the hind limb of a frog and place the limb in the volume 

 tube. Hook electrodes into the muscle at opposite ends of the limb. 

 Fill the tube quite full of isotonic NaCl solution, and replace stopper 

 in such a way that air is absolutely excluded and fluid is forced 

 part way up the capillary tube. Ajust the position of the meniscus 

 by the glass rod. Stimulate the muscle by an interrupted induction 

 current. Note movements, if any, of the meniscus and draw 

 conclusions as to the nature and extent of the change of volume 

 during contraction. 



C. GRAPHIC RECORD OF CONTRACTIONS. 



189. The graphic method of recording muscular contractions and 

 other physiological processes. The muscle is so arranged that its own 

 contraction describes en a uniformly moving surface a curve from 

 which the extent, character and time-relations of the movement 

 can be seen. Usually smoked paper is used wrapped around a drum 

 on a vertical axis moved by clock work. Such an instrument is 

 a kymograph. Examine thoroughly. Learn how to wind it, regu- 

 late speed, etc., from the description in the Harvard Apparatus 

 Company catalogue. Learn how to cover the drum with paper and 

 smoke it. 



Examine also the following pieces of apparatus and learn their 



use : Light muscle lever, writing lever, scale pan and signal magnet. 



To prevent drying during experimentation, the muscle is often kept 



