95 



there is a difference in excitability at any point. There is 

 usually one or two such points. Locate them. 



Determine this by the chang-e produced in the muscular 

 effect, such as an increase, decrease or absence of contraction. 



Now cut the nerve at its spinal orig-in, and compare the 

 excitability at the cut end with that at a point near the 

 muscle. Repeat this from time to time. The cut end will 

 soon show a g-reater excitability which will decrease later 

 until it is completely lost. 



A dying- nerve first rises and then falls in excitability and 

 finally loses it altogether. A nerve undergoing the process 

 of drying becomes for a time, more irritable for this reason. 



336. Dead Muscle and Nerve. Immerse a nerve- 

 muscle preparation for a few minutes in warm water (40 

 degrees C). Apply all of the preceding stimuli and compare 

 results with those obtained from a normal preparation. 



337. Kuehne's Sartoeius Experiment. Carefully 

 dissect out the sartorius muscle, and to the tendon which 

 attaches it to the tibia tie a fine thread. The upper end of 

 the muscle may be freed from its attachment to the symphysis. 

 Suspend the muscle with its upper end hanging downward 

 and bring up under it a little glycerin in a watch-glass until 

 the end of the muscle just touches the glycerin. Observe for 

 a minute or two. No contraction should result. Cut off the 

 end which has touched the glycerin and note that the muscle 

 contracts as a result of the mechanical excitation. Again 

 touch the cut surface with glycerine and observe. If only 

 about one millimeter has been cut off there is again no con- 

 traction. Cut off a fresh millimeter of muscle and repeat as 

 before. It will be found that when about three or four milli- 

 meters of the cephalic end have been cut away, on contact of 

 the freshly exposed end with the glycerin, the muscle shows 

 irregular twitchings and is at last thrown into a state of incom- 

 plete tetanus. 



This experiment should be completed by showing that if 

 a gastrocnemius nerve-muscle preparation be made and the 

 cut end of the nerve dipped into glycerine, the gastrocnemius 

 is thrown into a similar series of irregular twitching. Nerve 

 fiber is therefore excitable to glycerin. The same experiment 

 may be tried upon a curarized muscle. 



