658 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



then, that the degree of contraction of arteries having no nervous 

 connection with the spinal cord, will to some extent vary with the 

 temperature, the state of nutrition, and so forth. 



Whether an area, the vasomotor nerves of which have been cut, is 

 at any moment warmer than the corresponding area of the opposite 

 side of the body, clearly must depend upon a number of independent 

 variables. Since the vessels on the intact side are still under the 

 influence of the central nervous system, they will at times be fully 

 contracted and at times fully dilated. On the cut side the variation is 

 relatively slight. It follows, then, that the tissues on the uncut side will 

 sometimes be warmer and sometimes be colder than on the cut side. 

 And it was shown by Schiff that, after extirpation of the superior 

 cervical ganglion on one side, the ear on the opposite side ordinarily 

 the cooler became the warmer when the animal was placed in a 

 heated chamber, when it became hot from exercise, when a feverish 

 condition was induced, and in certain emotional states. On the 

 cut side there was also an increase in temperature, but com- 

 paratively a slight one. Similar facts are known with regard to the 

 limbs. 



The more or less complete recovery of tone which we have just 

 spoken of might conceivably be due to a peripheral nervous mechanism, 

 and not, as we have suggested, to the inherent nature of the muscular 

 tissue. This we will consider in a later section (p. 671). 



What has been said above for the cat and dog, with regard to the 

 cervical sympathetic and the superior cervical ganglion, holds also for 

 man. The paralytic effects of section of the cervical sympathetic 

 continue indefinitely, but they diminish in intensity ; the recovery is 

 greater in the blood vessels of the ear and face than in the dilator 

 pupillse. 1 The presence of sweat glands on the face allows an 

 additional point to be noticed, namely, the permanent absence of 

 secretion of sweat on the side of the lesion. In some cases it has been 

 observed that, during exercise, when the face on the sound side flushes, 

 the face on the side of the lesion becomes paler. This is probably a 

 mechanical effect, the general flushing causing a lowering of blood 

 pressure. 



EFFERENT PRE-GANGLIONIC FIBRES IN RELATION TO THE ANTERIOR 

 AND POSTERIOR BOOTS OF THE SPINAL NERVES. 



The efferent fibres which pass from the spinal cord to the 

 sympathetic ganglia and to the pelvic nerve 2 (nervus erigens) form, in 

 mammals at any rate, no exception to the law of Bell and Magendie. 

 They pass outwards in the anterior and not in the posterior roots of the 

 spinal nerves. This is shown both by the absence of effect on stimulat- 

 ing the peripheral ends of the posterior roots, and by the absence of 

 degeneration 3 in the peripheral ends of the posterior roots when they 

 are cut. 



It is true that Strieker and others have found in the dog a rise of 



1 The recovery of tone in the blood vessels appears often to be complete ; this suggests 

 either that partial regeneration of the cervical sympathetic has occurred, or that some vaso- 

 motor fibres take a path other than that of the cervical sympathetic. 



2 Cf. below, p. 666. 



3 Of. Sherrington, Journ. PhysioL, Cambridge and London, 1897, vol. xxi. p. 209. 

 References to early work on degeneration in the nerve roots are given in this paper. 



