368 PHYSIOLOGY CHAP. 



Hirschmann (1863) observed that nicotine has a paralysing 

 action on the sympathetic system ; in the rabbit the intravenous 

 injection of nicotine abolished the effects of stimulating the 

 cervical sympathetic. But the methodical application of this 

 discovery is due to Langley and Dickinson (1889-90). They 

 established the fact that stimulation of the nerve roots that give 

 off sympathetic fibres is totally ineffective after injecting nicotine 

 into the circulation of a rabbit or cat. From this they concluded 

 that at some point of the system nicotine blocks the transmission 

 of the excitations passing towards the periphery. But when the 

 nerve-fibres behind a ganglion (i.e. peripheral to it) are excited, all 

 the effects observed previous to the injection of nicotine can be 

 obtained, showing that the point attacked by the poison lies within 

 the ganglion. This conclusion is confirmed by the fact that the 

 local application of a dilute solution of nicotine (about 0'5 per 

 cent) to the ganglia produces the same effect. 



The importance of this method may be illustrated by one of 

 Langley's experiments. Stimulation of the sympathetic immedi- 

 ately below the stellate ganglion produces, as is well known, 

 contraction of the blood-vessels as well as other changes in the 

 fore -limb and shoulder, and vaso-constriction, dilatation of the 

 pupil, and other effects in the head. After the application of a 

 dilute solution of nicotine to the ganglion, stimulation of the sym- 

 pathetic below it produces no effect in the fore-limb or shoulder, 

 but the usual effects in the head, while the effects of stimulation 

 on this side of the ganglion are unaltered. This shows that the 

 sympathetic fibres that supply the fore-limb are connected with 

 the cells of this ganglion, while those that supply the head pass 

 through the ganglion uninterrupted. On the other hand, if a 

 dilute solution of nicotine is applied to the superior cervical 

 ganglion and its accessory ganglion, stimulation of the sympathetic 

 below the stellate ganglion produces no effects in the head ; all the 

 fibres that pass through the stellate ganglion to supply the head 

 must therefore be connected with the cells of the superior cervical 

 ganglion or its accessory ganglion. 



Langley made similar experiments on other portions of the sym- 

 pathetic system, and also on the related bulbar and sacral nerves, 

 and came to the general conclusion that every efferent fibre of the 

 sympathetic system which runs from the cord in a white ramus 

 communicans ends without exception in a vertebral (lateral) or 

 pre-vertebral (collateral) ganglion, where it enters into direct 

 relations with a ganglion cell, which, by its non-medullated 

 process, transmits the impulse which it receives from the medullated 

 fibre towards the periphery. 



Langley distinguishes the nerve-fibres that end in the ganglion, 

 i.e. pre-ganglionic, from those which originate in the cells of the 

 ganglion itself, or post-ganglionic. Von Kolliker preferred the 



