NUMBER OF NERVE CELLS. 683 



It is hardly necessary to consider the evidence in detail, its general 

 nature is indicated by what has already been said with regard to these 

 ganglia. 



We have good evidence, also, that the fibres given off by these ganglia 

 run to the peripheral termination, without having nerve cells on their 

 course. 



Consequently, if a pre-ganglionic fibre has more than one nerve 

 cell in its course, the second or other additional cells must be in the 

 same ganglion as the first nerve cell, and the total number of cells with 

 axons terminating in the ganglion must be great. But such arrangement 

 is entirely unsupported by histological appearances. We may conse- 

 quently adopt the simpler view, that a nervous impulse, in passing from 

 the central nervous system to the periphery, passes through one nerve 

 cell only. 



The two questions, of the number of autonomic nerve cells on the 

 course of a nervous impulse, and of the presence of commissural fibres, 

 are closely connected. For if commissural fibres exist, and if they can 

 be put in action by the pre-gangiionic fibres, it follows that a nervous 

 impulse on its way to the periphery must in some cases, at any rate, 

 traverse more than one nerve cell. The facts which bear on the ques- 

 tion of commissural fibres are of several kinds. 



1. We may consider, first, some cases in which it can be shown that 

 commissural fibres do not exist. We have seen that the nerve cells of 

 the ganglion stellatum in the cat send vasomotor and secretory fibres 

 to the fore-foot, and vasomotor and pilo-motor fibres to the skin of the 

 lower part of the neck and upper part of the thorax. If the superior 

 cervical ganglion sends commissural fibres to any of these nerve cells, 

 stimulation of the central end of the cervical sympathetic must cause 

 observable changes in the foot and in the skin of the back. In fact, the 

 stimulation has no effect. It is clear, then, that the superior cervical 

 ganglion does not send commissural fibres to the great majority of cells 

 of the ganglion stellatum. And, so far as the experiments have gone, it 

 does not send commissural fibres to any of the cells of the thoracic 

 ganglia. 



The inferior cervical ganglion is small and comparatively unimportant, 

 but as it is placed near the ganglion stellatum, it might be expected to 

 send fibres to this ganglion. On stimulation of the central ends of the 

 annulus of Vieussens — the white rami being cut — I have not found any 

 effect on the blood vessels or glands of the foot, or on the hairs of the 

 back ; so that the inferior cervical ganglion sends no commissural fibres 

 to those nerve cells of the ganglion stellatum which govern the above- 

 mentioned structures. 



Stimulation of the sympathetic chain, just above the first coccygeal 

 ganglion, has no effect on the hairs or blood vessels supplied by the 

 lumbar or by any higher ganglia, so that the first coccygeal ganglion 

 does not send fibres to the vasomotor or pilo-motor cells of these 

 ganglia. 



Stimulation of the upper thoracic region of the sympathetic does not 

 affect the lumbar ganglia ; nor does stimulation of the lumbar region 

 affect the upper thoracic. These parts of the sympathetic cannot then 

 be joined by commissural fibres. 



So far, we have spoken of the ganglia of the sympathetic chain. 

 There are similar facts with regard to the pre-vertebral and the vertebral 



