636 THE AUTONOMIC NERVOUS SYSTEM 



of relay centers. As such they effect a considerable increase in 

 the number of the efferent channels, because when the preganglionic 

 path terminates in a certain sympathetic ganglion, its fibers arborize 

 and form various new connections with these cells. The postganglionic 

 path, therefore, must be numerically stronger than the preganglionic. 

 A similar multiplication of paths results in the next ganglion and so on 

 until the periphery has been reached, where we find such intricate 

 ramifications of fibers as the plexuses of Meissner and Auerbach, or the 

 plexus cardiacus. Obviously, this fan-like expansion of the primary 

 path into multiple secondary and tertiary paths, enables the principal 

 center to control a large number of effectors and a wide area of tissue. 

 In the second place, it renders the distal ganglia and plexuses partially 

 independent of the cerebrospinal centers, because they can intercom- 

 municate with one another without that the impulses need be relayed 

 within the cerebrospinal system. 



The formation of these relatively local centers for the control 

 of particular processes, necessitates the development of a certain 

 number of afferent channels, without which the motor actions could not 

 attain the preciseness required of them. While it cannot be doubted 

 that these afferent elements are present, it must be admitted that they 

 are fewer in number and retain for the most part a local importance. 

 It is also evident that their number varies considerably in different 

 parts of the autonomic system. This must necessarily be so because 

 certain structures, such as the glands along the intestinal tract, re- 

 quire a closer functional correlation than other organs. In general, 

 it may be said that these afferent sympathetic neurons serve two 

 purposes, namely, to effect perfectly local reflexes and to consummate 

 reactions in parts remote from the seat of the stimulation. In the 

 latter case, the impulses may even enter consciousness and give rise 

 to voluntary actions. This, however, is rather the exception. To 

 illustrate, the stomach or intestine may be excised and if kept under 

 proper conditions of moisture and temperature, may be made to move 

 and to secrete in a manner not widely different from normal. This 

 implies that these organs are in possession of local nervous mechanisms, 

 consisting of afferent and efferent arcs and their corresponding end- 

 organs, which enable them to continue their actions even when iso- 

 lated from the cerebrospinal system or from neighboring sympathetic 

 ganglia. But it is also evident that these organs are constantly sub- 

 jected to stimuli arising elsewhere in the autonomic system or even 

 in the cerebrospinal system itself. Thus, a flow of gastric juice or of 

 any other digestive secretion may be evoked by stimuli arising else- 

 where in the abdominal cavity or in the receptors of the mucous mem- 

 brane of the mouth, the taste-buds, olfactory cells, and others. The 

 fact that the different sympathetic paths contain afferent fibers, finds 

 ample proof in the pressor and depressor reactions following in the wake 

 of the excitation of the hepatic and mesenteric plexuses. * It may be 

 1 Burton-Opitz, Quart. Jour, of Exp. Physiol., iv, 1911, 93. 



