644 NERVOUS SYSTEM. 



These experiments show that certain impressions made upon the sensory 

 nerves affect the animal heat, by reflex action. As section of the sympa- 

 thetic filaments increases the heat in particular parts, with an increase 

 in the supply of blood, and their Faradization reduces the quantity of blood 

 and diminishes the temperature, it is reasonable to infer that the reflex 

 action takes place through the vaso-motor nerves. If it be assumed that 

 the impression is conveyed to the centres by the nerves of general sensibility, 

 and that the vessels are modified in their caliber and the heat is affected 

 through the sympathetic fibres, it remains only to determine the situation of 

 the centres which receive the impression and generate the stimulus. These 

 centres are situated in the cerebro-spinal axis. 



The existence of vaso-motor nerves and their connection with centres in 

 the cerebro-spinal axis are now sufficiently well established. It is certain, 

 also, that centres presiding over particular acts may be distinctly located, as 

 the genito-spinal centre, in the spinal cord opposite the fourth lumbar verte- 

 bra, and the cilio-spinal centre, in the cervical region of the cord. An im- 

 pulse generated in these centres, sometimes as the result of impressions re- 

 ceived through the nerves of general sensibility, produces contraction of the 

 non-striated muscular fibres of the iris, vasa deferentia etc., including the 

 muscular walls of the blood-vessels. The contraction of the muscular walls 

 of the vessels is tonic ; and when their nerves are divided, relaxation takes 

 place and the vessels are dilated by the pressure of blood. By this action 

 the local circulations are regulated in accordance with impressions made 

 upon sensory nerves, the physiological requirements of certain parts, mental 

 emotions etc. Secretion, the peristaltic movements of the alimentary canal, 

 the movements of the iris etc., are influenced in this way. This action is 

 also illustrated in cases of reflex paralysis, in inflammations as the result of 

 " taking cold," and in many other pathological conditions. 



It remains only to show that the phenomena following section of the 

 sympathetic in animals are illustrated in certain cases of disease or injury in 

 the human subject. It is rare to observe traumatic injury confined to the 

 sympathetic in the neck. A single case, however, apparently of this kind, 

 has been reported by Mitchell. A man received a gunshot-wound in the 

 neck. Among the phenomena observed a few weeks after, were contraction 

 of the pupil on the side of the injury, and after exercise, flushing of the face 

 upon that side. There was no difference in the temperature upon the two 

 sides during repose, but no thermometric observations were made when half 

 of the face was flushed by exercise. Bartholow has reported several cases of 

 unilateral sweating of the head (two observed by himself), in several of 

 which there probably was compression of the sympathetic, from aneurism. 

 In those cases in which the condition of the eye was observed, the pupil was 

 found contracted in some and dilated in others. In none of these cases 

 were there any accurate thermometric observations. In a series of obser- 

 vations by Wagner, upon the head of a woman, eighteen minutes after 

 decapitation, powerful stimulation of the sympathetic produced great en- 

 largement of the pupil. In such a case as this, it would not be possible to 



