AFFERENT AUTONOMIC FIBRES. 687 



type of posterior root cell, namely, one which has the general characters of 

 Golgi's " sensory " type. The cell is small, its axon divides into a 

 number of branches, and each branch ends in connection with typical 

 unipolar cells. Thus Dogiel considers that a few afferent sympathetic 

 fibres can stimulate a considerable number of posterior root cells. It 

 will be noticed that a point of primary importance, namely, the origin 

 of the branching fibres from the sympathetic, rests on wholly insufficient 

 evidence. Dogiel's theory must be regarded as purely provisional, for 

 there are certain facts which are inconsistent with it. Section of the 

 inferior splanchnics, 1 the lower lumbar sympathetic chain, 2 or of a white 

 ramus 2 does not, as a rule, cause degeneration of any medullated fibres 

 in the central ends of the nerves. Sometimes a few degenerated fibres 

 may be followed for a short distance, but these appear to belong to small 

 grey bundles and to pass off to peripheral tissues. This, of course, 

 requires close investigation. The result, however, tends to show that 

 the pre-vertebral ganglia do not send any medullated fibres to end free 

 in the spinal ganglia, and that the vertebral ganglia do not send any by 

 a white ramus. The result does not exclude the possibility of medullated 

 fibres passing from a vertebral ganglion to a spinal ganglion by a grey 

 ramus, but the absence of physiological evidence of the presence of 

 sensory fibres in the grey rami is against it. 



We may at any rate conclude that the majority of the afferent 

 sympathetic fibres have their trophic centre in the cells of the spinal 

 and not in the sympathetic ganglia. 



It is well to bear in mind that the evidence, that the fibres between the 

 spinal cord and the sympathetic chain are all medullated, is not entirely 

 conclusive. The evidence simply establishes a high degree of probability. 

 Beck (1846) describes a few "gelatinous" fibres in both anterior and posterior 

 roots. Gaskell does not find any in the anterior roots, but does find some in 

 the posterior roots. No doubt the probability is, that such non-medullated 

 fibres as occur in the nerve roots run to the blood vessels of the spinal cord, 

 but the proof of this is defective. 



Relative number of afferent and efferent fibres. — The number of 

 efferent and of afferent medullated fibres in a nerve strand can be deter- 

 mined by cutting the anterior roots of the nerves which supply it, and 

 counting later the number of degenerated and of sound fibres. By this 

 method, it appears that about one- tenth only of the medullated fibres in the 

 hypogastric nerves are afferent, 3 and the proportion of afferent fibres in 

 the several splanchnic nerves is probably not very different from this. 

 In the pelvic nerve, the proportion of afferent fibres is considerably 

 greater, and in the cat approximately one-third of the whole number. 4 



The cervical sympathetic contains no afferent fibres proper to it, for 

 stimulation of its central end does not cause pain, nor any reflex action. 

 Sometimes a few afferent fibres from the vagus join the cervical 

 sympathetic, but they run down the neck, and do not accompany the 

 nerve in its peripheral course. The grey rami of the vertebral ganglia 

 have also few, if any, afferent fibres accompanying the efferent post- 

 ganglionic fibres to their peripheral endings. 



1 Langley and Anderson, Journ. Physiol., Cambridge and London, 1S94, vol. xvii. p. 184. 

 - Langley, ibid., 1896, vol. xx. p. 55. 



3 Langley and Anderson, ibid., 1894, vol. xvii. p. 185. 



4 Ibid., 1895, vol. xix. p. 377. 



