ADVANCED EXPERIMENTAL PHYSIOLOGY 329 



the threads of the unpolarisable electrodes are tied gently, one to each 

 end of the muscle. The conductivity of the threads is maintained by 

 the saline kaolin. The unpolarisable electrodes are connected by a 

 Du Bois key with a rheochord and Daniell cell. 



On closure of the current the lever attached to the kathodic end will 

 move first; the contraction starts in this 

 portion of the muscle and spreads through 

 the length of the sartorius. On break of ^z: 



the current the other lever, the one attached 



to the anodic end of the muscle, will move 



first. The direction of the constant current FIG. 207. -A screw clamp which 



can be made to serve the purpose 



should be reversed and the experiment re- of a Gaskeirs damp. TWO small 



* wedges of cork are fixed one to 



peated, SO that a Control may be placed the lowest bar and the other to 



J the moveable bar. 



upon the results. 



If a graphic record be taken, the levers should be of equal length so 

 that their writing points will mark the one vertically under the other. 



Engelmann's Experiment. The other sartorius muscle of the 

 curarised frog is dissected out with a piece of the pelvic girdle and is 

 suspended by fixing a pin through the bone ; the kaolin plugs of the 

 unpolarisable electrodes are replaced by two new plugs so arranged 

 that the constant electrical current can be made to pass transversely 

 across the pelvic end of the muscle. When the current is made, the 

 free end of the muscle moves towards the kathodic side ; but towards 

 the anodic side when the current is broken. 



Biedermann's Experiment. The sartorius muscle is carefully dis- 

 sected from a pithed frog and is left attached to the pelvic girdle. 

 The surface of the muscle is gently dried with filter-paper and then is 

 striped transversely with equidistant black lines ; for this purpose a 

 fine paint-brush, or bristle, and black water-colour paint are used. The 

 thread of one unpolarisable electrode is placed on the muscles of the 

 frog's abdomen, the thread of the other electrode is brought into con- 

 tact with a portion of the striped sartorius. The unpolarisable elec- 

 trodes are connected with a Daniell cell by a Du Bois key. 



In the first place let the electrode applied to the sartorius muscle be 

 the anode. On closure of the electrical current the black lines 

 can be seen with a lens to recede from one another; the muscle 

 relaxes in the anodic region. Anelectrotonus causes a decrease in 

 excitability; the tone of the muscle is diminished. The direction of 

 the constant current is now reversed : on closure the black lines 

 approach one another; the muscle contracts in the kathodic region. 

 Katelectrotonus produces a rise in excitability ; the tone of the muscle 

 is increased ; it contracts. 



