UNSTRIATED MUSCLE 47 



the minimal tetanising current which will cause contrac- 

 tion when applied to the end of the nerve. Brush 1 p.c. 

 cocaine over the end of the nerve for about 1J cm. and 

 stimulate at intervals of about 3 mins. till moderately 

 strong currents applied at the end of the nerve have no 

 effect; the lower part of the nerve must not be raised 

 from the moist paper, or there may be sufficient escape 

 of current to it to cause contraction. Place the prepara- 

 tion in saline solution and in 15 to 30 mins. stimulate 

 again; the time required for recovery is however often 

 long. 



Point of action of NaCl twitching s. Rinse in saline 

 solution the sartorius which has been in curari ; place it, 

 and the other sartorius which has been in saline solution, 

 in pure NaCl -6. Both will twitch, but the curarised 

 muscle probably less than the other. Thus the NaCl 

 twitchings are due to an action on the general muscle 

 substance. When the twitchings have developed, place 

 the muscle in saline solution to stop the twitchings, and 

 transfer to ] p.c. nicotine; the curarised muscle will not 

 contract, so that in this case the action is not on the 

 general muscle substance. 



Twitchings caused by guanidim. Rinse in saline solu- 

 tion the foot which has been in curari and place both 

 feet in about 20 c.c. of guanidine chloride 05 p.c. The 

 uncurarised muscle will twitch, the curarised muscle 

 will not. Thus in this case the twitchings are due to an 

 action in the region of the nerve endings. 



Brief twitchings are caused in frog's muscle by dilute nicotine 

 (-001 -1 p.c.) and long continued twitchings in mammalian muscle 

 by physostigmine. Both are prevented by curari. 



