THE SYMPATHETIC NERVE. 577 



Kespecting the influence of the sympathetic nerve in 

 nutrition and secretion, we may refer to the chapters on 

 those processes. The mode in which this influence is exer- 

 cised is still obscure, though probably it is in a great 

 measure exercised through the vaso-motor nerves (p. 153), 

 and is, therefore, connected with the supply of blood to 

 the parts. The experiments of Bernard, Waller, Brown- 

 Sequard, and others, render it certain that the sympathetic 

 nerve possesses great influence over the contractile power 

 of the blood-vessels, division of the trunk or branch of 

 such nerve being followed by paralysis of the muscular 

 coat of the vessels supplied by the ramifications of the 

 divided nerve, and by consequent congestion and increased 

 temperature of the parts in which such vessels are distri- 

 buted ; while galvanic or other stimulus to the nerve is 

 followed by contrary effects, namely, by contraction of the 

 vessels, and by diminution in the quantity of blood and ir 

 temperature. So constant and important are these results, 

 that the sympathetic nerve may be regarded as having, 

 for its principal office, the power of regulating and con- 

 trolling the supply of blood to parts, its fibres constituting 

 the true vasomotor nerves. Besides acting directly upon 

 the muscular coat of the vessels, and thus determining the 

 supply of blood, the sympathetic may possibly also influence 

 the nutritive and secretory changes in a part by direct 

 action on its tissue, whereby it is stimulated to increased 

 activity of function ; for the changes in the mode of nutri- 

 tion and secretion in a part cannot be altogether explained 

 by mere variations in the diameter of its blood-vessels, or 

 in the quantity of blood supplied to it. Daily observation 

 shows multiform results in secretion and nutrition in cases 

 of disease, of which all have, as a common condition, the 

 enlargement of the blood-vessels of the diseased part ; 

 something, therefore, besides the enlargement of the ves- 

 sels, must in these cases determine the different events : 

 and so when the various exercise of nervous influence in a 



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