668 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



5 /a in diameter. In the rabbit the pelvic nerve has few fibres other than 

 small. The histological characters of the nerve cells in the course of the 

 pelvic nerve are, so far as is known, the same as those of the sympathetic 

 ganglia. 



The Enteric Nervous System. 



The plexuses of Auerbach and Meissner are peculiar to the gut ; 

 they extend from the beginning of the unstriated portion of the 

 oesophagus to the end of the rectum! They have usually been con- 

 sidered to belong to the sympathetic system, but it appears to me 

 preferable to place them in a class by themselves. We may speak of 

 them as forming the enteric nervous system. The chief reasons for 

 placing the enteric nerve cells in a class by themselves are, first, that they 

 differ in many of their histological characters from the nerve cells of 

 the vertebral and pre-vertebral ganglia ; and, secondly, that we do not 

 know whether they are connected with the central nervous system by 

 sympathetic or by cranial and sacral autonomic fibres. 



The injection of a certain amount of nicotin into a blood vessel in a 

 rabbit prevents stimulation of the spinal nerves having any effect upon 

 the intestine, so that nicotin paralyses all the pre-ganglionic fibres. 

 The results of local application of nicotin to the inferior mesenteric 

 ganglion gives evidence that the pre-ganglionic fibres for the gut end in 

 the pre-vertebral ganglia. If these impulses pass to the enteric nerve 

 cells from the central nervous system, by way of the sympathetic, they 

 must pass by the post-ganglionic fibres of the pre-vertebral ganglia. 

 But the injection of nicotin does not prevent stimulation of the post- 

 ganglionic" fibres from producing their usual effects, so that either the 

 post-ganglionic fibres send collaterals only to the enteric cells, or, if they 

 end entirely in synapses with the enteric cells, the synapses are not 

 paralysed by nicotin. In either case, the arrangement is different in 

 the enteric and in the sympathetic (vertebral and pre-vertebral) 

 ganglia. In view of this, it is natural to suppose that the enteric 

 cells are in the course of the vagus fibres in the upper part of the gut, 

 and in the course of the sacral fibres in the lower part of the gut. The 

 matter has not been sufficiently investigated to allow any decisive 

 opinion to be arrived at. The experiments that have been made have 

 been chiefly on the lower part of the gut ; the results have tended to 

 show that the sacral fibres end in cells of the sympathetic type, and 

 not in the cells of the enteric plexuses. 



Possible Autonomic Fibres running direct in the 

 Cerebro-Spinal Nerves. 



The view that some vasomotor fibres leave the cord by the roots of a 

 spinal nerve, and accompany the branches of the spinal nerve to the periphery, 

 is an old one, but no definite experiments were alleged in support of it before 

 Schiff's account of the innervation of the vessels of the ear and of the vessels 

 of the limbs. 



There are one or two general considerations with regard to these fibres 

 which must be borne in mind. 



If such fibres exist in the particular cases mentioned, we should expect to 

 find them in every spinal nerve, for there is nothing in the function of the 

 nerves to the ear or limbs which makes it reasonable to suppose that they have 



