58 EXPERIMENTAL PHYSIOLOGY. 



muscle is frequently reached in a few definite steps. The number 

 of steps is never greater than the number of motor nerve fibres sup- 

 plying the muscle. The cutaneous dorsi nerve of the frog contains 

 only eight nerve fibres and each nerve fibre supplies a large num- 

 ber of muscle fibres, 150 to 200. Lucas found that upon gradually 

 increasing a stimulus to this nerve from sub-minimal to supra- 

 maximal that there were never more than eight steps in the height 

 of muscular contraction. 



Experiment 27. Adrian's Experiment. The object of this 

 experiment is to determine whether a nerve impulse which is 

 reduced in strength by passing through an area of narcosis can 

 regain its strength on entering a normal part of the nerve fibre. 

 A large frog should be selected and from it two nerve muscle 

 preparations made, taking care not to injure the nerves and to 

 procure their entire length from their origin in the cord. 



It is unnecessary to arrange recording apparatus for this 

 experiment. The narcotizing chamber, Fig. 16a, should be 

 carefully dried and placed on a dry glass plate. The glass dome 

 of the moist chamber should be lined with moist filter paper 

 so that it may be used to cover the preparation during the 

 experiment. Arrange inductorium so that single induced shocks 

 may be obtained from the electrodes. The nerves are to be 

 laid along the grooves of the narcotizing chamber, their proximal 

 ends being in vaseline at the points where the grooves open into 

 the circular cups, and care taken that the grooves are dry so 

 that when the narcotic is introduced into the cups it will not 

 flow back along the grooves. 



When this is done regulate the strength of the stimulus so 

 that the muscles respond maximally to break shocks, but do not 

 respond to make shocks. Now introduce enough 15% alcohol 

 made up in Ringer's fluid into the cups of the moist chamber. 

 At 20 second interval stimultae the preparations, watching to 

 see if either of them fail, to contract. Determine how long each 

 one continues to respond. 



When the first preparation fails to respond to a single shock 

 try sending in a series of shocks in as rapid succession as possible. 

 If a response occurs it is due to summation in conduction. 

 How is it explained? 



