88 



of the nerve elevated to the mouth of the tube. There should 

 be no contraction if the vapor has not come in contact with 

 the inuscle. The ammonia kills the nerve. Apply ammonia 

 to the muscle. It contracts. 



323. Electrical. For the following experiments, use the 

 other leg of the frog, taking the same precautions in the dis- 

 section and application of the normal salt solution. 



(a) Arrange the nerve-muscle preparation with the fe- 

 mur in a clamp and connect with a recording lever. Arrange 

 the battery and DuBois Reymond Key with the induction coil. 

 Connect the battery wires with the primary coil and remove 

 the secondary coil to the lower end of the scale. Arrange the 

 electrodes with a short-circuiting key and a recording drum 

 with smoked paper, conveniently to the preparation.. When 

 all is in readiness, close the connection by means of the key 

 by raising or lowering its lever. Or in other words " making " 

 or "breaking" the current. Gradually move the secondary 

 coil along the scale while making and breaking the current. 

 The current is made when the connection is complete, and 

 broken when the connection is interrupted. Note at what 

 point on the scale llie first result appear^-'ud whether it be 

 from " make " or " break." Make a table of your results as 

 follows : In one column indicate the distance of the second- 

 ary coil from the primary. In another, Response at Make, 

 and the last column. Response at Break. This is electrical 

 stimulation in the form of single induction shocks. The highest 

 tracings represent maximal and the lowest minimal stimuli. 

 Submaximal stimuli represent any strength between these 

 two extremes. 



(b) Remove the induction coil and use olittly the battery 

 with its wires and the key. Make and break the current as 

 in (a). Notice that if the key be so affgfff^ed as to permit 

 the current to flow continuously through the nervej no con- 

 traction occurs, provided there be no variation in the intensity 

 of the current. Rapidly make and break the current by open- 



-" and closing the key ; a more or less perfect tetanus is pro- 

 duced. This i&-the constant current form of stimulation. 



(c) Remove the wires from the primary coil and connect 

 them with the sockets leading to the vibrating hammer. On 

 applying the electrodes to the nerve or muscle the latter is at 



