BY DR. BURDON-SANDERSON. 257 



55. (1.) Demonstration of the Vasomotor Functions 

 of the Cervical Portion of the Sympathetic Nervous 

 System in the Rabbit. In 1852, Brown-St'quard showed 

 that when the sympathetic nerve is divided in the neck, the 

 central artery of the ear dilates, and the organ becomes vascu- 

 lar ; and that when the peripheral end is excited, the same ar- 

 teries contract ; and in the same year he demonstrated that 

 the former effect was dependent on paralysis, the latter on 

 spasm of the muscular walls of the vessels. 



A rabbit having been placed on the support in the prone 

 position, about four cubic centimetres of a five per cent, solu- 

 tion of chloral (obtained by diluting a stronger solution with 

 the required proportion of the ordinary solution of chloride of 

 sodium) is gradually injected into the crural vein. [For the 

 method of exposing the crural vein and of inserting the canula, 

 see 49]. As soon as the animal is insensible, an incision is 

 made about two inches in length parallel with the trachea, so 

 as to expose the edge of the sterno-mastoid muscle on one 

 side. The carotid artery is then brought into view, separated 

 from the vagus, and drawn forward from beneath the edges of 

 the muscle with the (fig. 203, c) hook, when it is seen that two 

 small nerves, both much smaller than the vagus, are drawn 

 forward with it, embedded in the membranous sheath (fig. 

 227). Of these two nerves, one, which is the smaller of the 

 two, is the depressor an important cardiac branch of the 

 vagus; the other is the sympathetic. To discriminate between 

 them, all that is necessary is to trace them both upwards. It 

 is then seen that the depressor arises by one root from the 

 vagus trunk, by another from the superior laryngeal ; whereas 

 the sympathetic continues its course upwards alongside of the 

 artery. The sympathetic is also distinguishable by its gray 

 color. A loose ligature having been placed round the nerve, 

 the condition of the posterior auricular artery should be care- 

 fully observed, and noted in the manner recommended in the 

 previous paragraph. On dividing the nerve, it is seen that 

 the artery dilates, the rhythmical movements cease, and the 

 whole vascular network of the ear rapidly becomes injected 

 with blood. The change in the condition of the organ is very 

 similar, both in degree and in kind, to that observed after ex- 

 citation of the central end of the auricular nerve, but differs 

 from it in being more permanent. If after a few minutes the 

 ears are held, one in each hand, it is felt that that of the in- 

 jured side is warmer than the other. If now the peripheral 

 end of the divided nerve is placed between the copper points 

 and the key opened, the artery contracts and the congestion 

 of the car disappears. 



This experiment shows conclusively that most of the spinal 

 vasomotor nerves which are distributed to the arteries of the 

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