174 Prof. J. N. Langley. On Nerve Endings and on [May 24, 



Now it cannot be denied that the great majority of the known facts receive 

 a satisfactory explanation on this theory. Moreover, certain facts — those 

 relating to the action of poisons on particular systems of nerves — are not 

 easily explained on any other. Nevertheless, some recent observations go 

 far to show that the theory is untenable. I will consider first the observa- 

 tions on motor nerve endings in striated muscle, since they are at present 

 the most complete, and then briefly review those which concern other nerve 

 endings. 



Nerve Endings in Striated Muscle. 



Nicotine is one of the many poisons which, in the usual acceptation of the 

 phrase, paralyses motor nerve endings in vertebrates. 



In some birds it has an additional action,* not so far observed in mammals. 

 It causes certain muscles to pass into a state of tonic rigidity, and to remain 

 in this state for many minutes. The contraction is not due to stimuli sent 

 out by the central nervous system, for it occurs when all the nerves 

 supplying the muscles are severed. If about 1 milligramme of nicotine, or 

 any larger quantity, is injected into a vein of an anaesthetised fowl, the hind 

 limbs, previously lax, gradually become stiff and extended (cf. figs. 1, 2, and 3), 

 and they may remain so for a quarter to half an hour, or even longer. 



When a graphic record of the contraction of a single muscle, such as the 

 gastrocnemius, is made, the shortening of the muscle is seen to take place 

 slowly and steadily to a maximum, which is approximately maintained for 

 several minutes ; this is followed by a gradual and much slower relaxation. 



Fig. 1.- — Fowl, anoesthetised with morphia and A.C.E. mixture, balanced on its thorax in 

 a V-shaped piece of wood. The neck and legs hang down and are flaccid, the 

 eyes are shut. 



* Langley, ' Journ. of Physiol.,' vol. 33, p. 380, 1905. 



