682 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



this ganglion does not stop them. Injection of nicotin, or local application of 

 nicotin to the superior cervical ganglion, does put a stop to them. We may 

 conclude, then, that the nerve cells which are set in action are in the superior 

 cervical ganglion, and that the reflexes are produced by fibres which divide in 

 the trunk of the sympathetic, one division running to the anterior and the 

 other to the posterior limb of the annulus of Vieussens. I have not found any 

 effect on the eye, when the central end of the nerve which is given off by the 

 ganglion stellatum to the heart and lungs is stimulated, although this contains 

 numerous sensory fibres. 



Francois-Franck also describes a reflex contraction of the pupil by way of the 

 long ciliary nerves and the ciliary ganglion. Anderson and myself made one or 

 two experiments on the cat and dog, but were unable to confirm this result. 



It has been mentioned above, that after degenerative section of the inferior 

 splanchnic nerves, stimulation of the central end of one hypogastric nerve has 

 no effect ; and we have deduced from this, that in all probability nervous 

 impulses in post-ganglionic fibres cannot travel back through nerve cells and 

 affect other nerve cells. It is clear, at any rate, that the impulses cannot excite 

 all the nerve cells in the ganglion, for in that case stimulation of the central 

 end of the hypogastric in the given circumstances would cause inhibition (or 

 contraction) and pallor of the descending colon and rectum, since the nerves 

 for those structures and the hypogastric nerve fibres arise in part from the 

 same ganglia. 



The experiment may also be taken as showing that the post-ganglionic 

 fibres do not divide and send a branch to each hypogastric nerve ; this makes 

 it probable that post-ganglionic fibres only divide near their terminations, and 

 thus we should not expect to find any wide spreading out of effects by an 

 action on post-ganglionic fibres, analogous to that which may be obtained by an 

 action on pre-ganglionic fibres. 



Some other experiments, to observe whether stimulation of the central end 

 of post-ganglionic fibres could cause a reflex effect, were made by Anderson and 

 myself. We found no effect on stimulating the central end of one of the short 

 ciliary nerves, nor on stimulating the central end of any one of the branches of 

 the superior cervical ganglion. 



On the Number of Nerve Cells on the course of a Pre-Ganglionic 

 Fibre, and on Commissural Fibres. 



In the preceding account I have assumed that a nervous impulse, in 

 its passage from the central nervous system to the periphery, passes 

 through one nerve cell only of the sympathetic type, and that such 

 nerve cells are not connected by commissural nerve fibres. Both of 

 these assumptions are opposed to general belief. Those who have 

 considered that the nervous impulses pass through nerve cells at all, 

 have taken for granted that in many cases they pass through more than 

 one nerve cell ; and most observers have taken for granted that the 

 sympathetic ganglia are connected by commissural fibres. In this 

 section I shall give some of the reasons in favour of my own view. In 

 doing so ; it must be remembered that I consider enteric nerve cells to 

 be of a different type from the sympathetic nerve cell. 1 



We have good evidence, in the case of particular ganglia, that all the 

 pre-ganglionic fibres which are able to affect the ganglion run to it 

 direct and end in connection with its nerve cells. This is, for example, 

 the case with the superior cervical ganglion, the ciliary ganglion, and 

 the coccygeal ganglion. 



1 Cf. p. 668. 



