THE AUTONOMIC NERVOUS SYSTEM 751 



ganglionic fibres before and after painting a ganglion with nicotine, 

 it is possible to determine which set of preganglionic fibres makes 

 connection with the cells of the painted ganglion. i^j 



By this means it has been found that the preganglionic fibres passing 

 out from the cord in the white ramus may either end at once in the 

 ganglion which they first enter, or pass upwards or downwards 

 to end in neighbouring lateral ganglia in the sympathetic chain, 

 or . pass through to connect with the abdominal group of col- 

 lateral ganglia. Each fibre has one cell-station in one ganglion, 

 and no more than one. The white rami emerge from the spinal cord 

 by the anterior roots of the second thoracic to the third lumbar 

 nerves. On examining microscopically cross-sections of these roots, 

 the sympathetic fibres are distinguished by their small size. The 

 grey rami which arise in the ganglia connected with these fibres do 

 not necessarily pass back to the spinal nerves coming from the same 

 segment of the spinal cord. Thus the white rami for the sympathetic 

 nerves to the fore-limb are the fourth to the tenth thoracic ; the grey 

 rami ascend to join the nerves of the cervical nerves forming the 

 brachial plexus. 



For this reason it is necessary to distinguish between the effect 

 of stimulation on a spinal nerve when it contains only the white ramus, 

 and the effect on the same nerve when it has received the grey ramus. 



The origin of the sympathetic fibres which supply each part has 

 been determined by stimulating the anterior roots of the spinal nerves, 

 Thes r contain only outgoing preganglionic fibres. 



The .Function of the Ganglia. The function of the ganglia is that 

 of distributing-stations, whereby the impulses destined for certain 

 parts are collected together into the appropriate efferent postganglionic 

 nerves. The execution of certain so-called reflex actions has been 

 ascribed to the ganglia, but these seem to be of the nature of the 

 reflexes concerned in paradoxical contraction, and are more correctly 

 termed " axon reflexes." The co-ordinate peristalsis of the intestine 

 is, however, carried out by the ganglionic plexus in its wall, and 

 this proves that this plexus has the power of executing functions of 

 the same order as those of the central nervous system. The destina- 

 tion, origin, cell-station, and effect, of the various efferent preganglionic 

 fibres may be summarized as shown in the first table on p. 752. 



The Cranial and Sacral Autonomic Systems. These are character- 

 ized by the length of their medullated preganglionic fibres, and by 

 the fact that the ganglia for the most part are situated either very 

 close to or actually in the organ supplied. For example, the ganglia 

 for the submaxillary and sublingual glands, are situated close to the 

 glands ; the ganglia for the cardiac fibres of the vagus are actually in 

 the heart itself. 



The cell-stations of these fibres can be traced by A the nicotine 

 method. For example, painting the sinu-auricular groove of the 

 frog's heart with nicotine abolishes the effect of the vagus nerve, but 

 not the effect of direct stimulation of the groove. On the contrary, 



