THE INHIBITORY NERVES 69 



from inhibitory nerve cells, just as fibres which contract involun- 

 tary muscle pass directly into the muscle from motor nerve 

 cells? 



It is well known that stimulation of the lumbar splanchnic 

 nerves causes relaxation of the musculature of the bladder, and 

 that the fibres' concerned end in cells of the inferior mesenteric 

 ganglion ; also that from these same cells fibres pass to the 

 bladder muscle itself, and cause relaxation of the detrusor urinae, 

 as is seen upon stimulation of the hypogastric nerve. Such cells 

 are, according to my view, inhibitory cells, giving off inhibitory 

 fibres directly to the muscle itself; and the actual proof that 

 these nerve fibres induce chemical changes of this nature in the 

 muscle is given by the action of adrenalin ; for adrenalin not 

 only causes relaxation of the bladder musculature in the normal 

 condition, but also, as Elliott has shown, relaxation of the 

 decentralized bladder, and still more markedly of the denervated 

 bladder. In order to denervate the bladder completely he 

 removed with the help of a lens all the nerve cells lying on the 

 surface of the bladder, and six weeks afterwards applied adrenalin. 

 This caused relaxation of the bladder, but no effect was caused 

 by stimulation of either the pelvic or hypogastric nerve. This 

 action of adrenalin on the denervated muscle, which is the 

 same as that caused by stimulation of the hypogastric nerves, 

 seems to me proof positive that these fibres of the hypogastric 

 nerve are inhibitory right into the muscle substance itself, and 

 that therefore involuntary nerve cells can give rise to inhibitory 

 nerves as well as motor nerves. 



I shall then speak of inhibitory nerves as well as motor 

 nerves and of inhibitory as well as motor cells, without implying 

 that they are always separate from each other, admitting, that is, 

 the possibility that a single nerve cell can give off both inhibitory 

 and motor fibres. 



The first question that requires an answer is: Have the in- 

 hibitory nerve cells of any particular muscular system travelled 

 out from the central nervous system in the same outflows as the 

 motor nerve cells of that system ? 



I will consider the vascular system separately and take first 

 the dermal system, the motor cells of which are found in the 

 ganglia of the lateral sympathetic chain. To this system belongs 

 the retractor penis muscle, an unstriped muscle which is inserted 



