EFFECT OF CURARE 77 



The action of the curare has been to destroy the physiological con- 

 tinuity of muscle with its nerve fibre. The poison injected is rapidly 

 absorbed into the blood, and so carried to all parts of the body with the 

 exception of the left leg below the ligature, where the vessels have 

 been occluded. The upper part of the left sciatic has been exposed to 

 the poison, but is still excitable, showing that the action of the poison is 

 not on nerve-fibre ; and as the muscles in any part of the body contract 

 when directly excited, it follows that they are not the parts affected 

 by the poison. The portion paralysed must therefore be situated at the 

 connection of the nerve to the muscle, i.e. the motor end plate or the 

 small terminal piece of nerve which is unprotected by a medullary 

 sheath. Just at this point, moreover, a very complex net of blood 

 vessels is found, so that the part would be freely exposed to any poison 

 present in the blood. 



From the same preparation we may also show another fact which 

 further tends to the same conclusion. 



Experiment 2. — Using single induced break shocks determine for the 

 left nerve the strength of stimulus necessary to just cause a twitch of the 

 gastrocnemius, and secondly that which gives a maximum twitch. Having 

 done this, apply the electrodes directly to the paralysed gastrocnemius, the 

 right, and determine the two corresponding positions for the muscle. 



It will be found that in the latter half of the experiment the stimulus 

 must be greater for both cases. This tends to confirm the previous 

 result, viz. that it is muscle fibre which is being stimulated, and not 

 nerve fibre, and in that case shows that MUSCLE IS LESS EXCIT- 

 ABLE THAN NERVE. 



Experiment 3. — Xuhne's Sartorius Experiment. — Carefully dissect 

 out a sartorius, 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 down- 

 wards, and bring up under it a drop of glycerine in a watch glass until the 

 end of the muscle just touches the glycerine. No contraction results. Cut 

 off the end which has touched the glycerine, and note that the muscle con- 

 tracts under the mechanical excitation. Again touch the cut surface with 

 glycerine. If only about 1 mm. of the end has been cut off there is a^ain 

 no contraction. Cut off a fresh miUimetre of muscle and repeat as before. 

 It will be found that when about 3 to 4 mm. of the upper (pelvic) end has 

 been cut away, on contact of the freshly exposed end with the glycerine, the 

 muscle shows irregular twitchings, and is at last thrown into a state of incon- 

 plete tetanus. This experiment should in the next place be supplemented 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 twitchings. Nerve fibre is therefore excit- 

 able to glycerine. 



The explanation of the preceding experiment becomes clear by the 



