CERTAIN SETS OF NERVES 95 



The pre-ganglionic fibers are those which connect the cord and the 

 ganglion-cell, while the post-ganglionic fibers are peripheral to the latter. 

 It appears that all the impulses given out by sympathetic fibers pass over 

 both of these paths. In other and more direct terms, it is not apparent 

 on the neurone theory that impulses originate in the sympathetic ganglia, 

 the presumption being rather that the exciting influence always comes 

 more or less directly from the central nervous system proper. Perhaps, 

 nevertheless, influences do originate in these ganglia as well as in other 

 knots of neuro-fibrils or masses of nerve-cell tissue. This problem is 

 still unsolved. The fact that, under abnormal conditions, the heart, for 

 example, may continue its beat after all "nerves" attached to it have 

 been "cut," does not prove that normally the organ does not receive 

 continually influences from the complex medulla, through these periph- 

 eral ganglion-cells. On the other hand, the same phenomena demon- 

 strate that either the heart-muscle or the nerve-cells within it have auto- 

 matic powers dependent on their own metabolism, at least for a time. 

 Between these two theoretic drifts the exact balance has not yet been 

 made : we do not know, in fine, how much or how little in the way of 

 actual energy-liberation the nervous system performs. If it liberates much 

 exciting energy we have no reason to deny to the cells of the sympathetic 

 their proportion of this essential work (e. g., in the heart or the uterus). 



The sympathetic, unaided by other autonomic nerves (see below) 

 actuates the bloodvessels, glands, and smooth muscles of the skin, the 

 bloodvessels of that part of the intestine between the mouth and the 

 rectum, of the glands opening into this portion of the gut, and possibly 

 also the spleen and the internal generative organs. In general terms, 

 then, if we may accept this estimate tentatively as correct, it is the func- 

 tion of the sympathetic to innervate much of the body's smooth muscle 

 tissue wherever its fabric, extending so widely through the body, occurs. 



For example, the pilomotors, the tiny muscles whose contraction 

 erects the hairs, are under this kind of influence. This suggests one 

 conspicuous way in which the sympathetic is controlled namely, 

 from the midbrain, at least in emotional conditions. The inhibitory 

 effects of the sympathetic action are as important, if not as widespread, 

 as those of the actual production of movement. A second possible 

 immediate duty of these nerves is still somewhat in doubt histologically 

 namely, the actuation of secretion directly by innervation of the secretory 

 protoplasm. If this connection between nerve and cell interior regularly 

 occurs, the sympathetic is the agent of the control. Where it does not 

 occur, on the other hand, secretory control is brought about through 

 vasomotion. As the sympathetic surely directs this process, secretion 

 in any case is under the management of this "system." 



But besides these two efferent functions (whether from the central 

 nerve-system or only from the sympathetic's vertebral or prevertebral or 

 peripheral ganglia) the sympathetic has minor afferent functions of various 

 sorts. These impulses pass inward apparently on both the gray and 

 the white rami, although only the latter, according to Langley, has been 



