672 THE NERVOUS SYSTEM 



for which we have proof of local reflex control. The regulation of the py- 

 loric sphincter through the acid control is an example of such local reflex. 

 This reaction takes place in the isolated organ. In certain ways the enteric 

 system seems to be most primitive in structure, comparable to the nervous 

 system we find in lower organism, such as anemones and medusae. How- 

 ever, the ganglion cells of this system have been proven to arise from the 

 neural groove and to migrate to their adult location during embryonic 

 development. Out of the investigations as to the function of these 

 mechanisms we have the idea of control represented in figure 41 9 A. 



According to Gaskell the functions of the main sympathetic ganglia are 

 the following: i. The sympathetic ganglia are aggregates of large numbers 

 of multipolar cells around which the medullated fibers of the white rami form 

 synapses. The branches of the cells are of the non-medullated fiber type. 

 Thus a medullated conduction is converted in the ganglia into a non-medul- 

 lated path beyond the ganglia. 2. The ganglion cells exercise a nutritive 

 influence over the tissues to which their fibers are distributed. 3. The num- 

 ber of preganglionic fibers entering the ganglia is not so great as that leaving, 

 since the cells are multipolar (not shown in the schematic figure 417). This 

 serves to multiply the influence of a relatively simple efferent preganglionic 

 conduction path and to extend it over a larger area the parts of which are 

 usually acting co-ordinatively. 



The sympathetic ganglia are not nerve centers in the usual sense. It is 

 better to regard them merely as distributing organs in which impulses of cen- 

 tral origin and comparatively simple type are distributed over relatively 

 large areas. These ganglia do not possess the power of reflex function 

 except in the enteric system as noted above. A type of pseudo-reflex 

 has been described depending on the law of neurone reaction. But it is 

 not supposed that such reflexes occur in the normal animal. 



Afferent Fibers in Sympathetic Paths. Afferent or sensory fibers of 

 the ordinary spinal-root ganglion cells are present in the sympathetic 

 nerves of the splanchnic region. These fibers are the distal branches of 

 posterior root ganglion cells and are distributed to the visceral region by 

 way of the white rami and the sympathetic system. These fibers have 

 their terminations in the mucosa of the alimentary and urogenital system 

 or in the muscular walls of these organs. Their stimulation arouses the 

 sensation of fullness (Hertz) that characterizes hollow organs, also sensa- 

 tions of pain and temperature as shown by Carlson for the stomach. It 

 is the stimulating influence of operative conditions on this class of sensory 

 fibers that plays so important a part in surgical shock. Modern practices 

 in anesthesia are especially devised to prevent this dangerous state of de- 

 pression. Such afferent paths are not a constituent part of the autonomic 

 classification of Langley. However, Dogiel has described a type of true 

 afferent sympathetic neurone. Their fibers arise from cells located in the 



