FUNCTIONS OF THE SYMPATHETIC SYSTEM. 435 



clear, alkaline liquid, colorless or slightly opaline, which pre- 

 cipitated a few flocculi of organic matter on boiling. 1 



Vaso-Motor Nerves. 



The experiments which we have already cited demonstrate} 

 beyond a doubt the existence of nerves distributed to the 

 muscular coats of the blood-vessels, and capable of regulating 

 their calibre and the quantity of blood sent to different parts. 

 These are the vaso-motor nerves, discovered by Brown-Se- 

 quard, in 1S52. 2 The importance of nerves capable of regu- 

 lating what we may call the local circulations is sufficiently 

 apparent. The glands, for example, require at certain times 

 an immense increase in their supply of blood, and the same 

 is probably true of the muscles, brain, and other parts. It 

 has been shown, by direct experiments upon living animals, 

 that local variations in the circulation, independent of the 

 action of the heart, actually take place, and that they are of 

 great importance in special functions ; and there are nu- 

 merous instances of such action, which can only take place 

 through the nervous system. The phenomena of blushing 

 and pallor, from mental emotions, are familiar examples. 



There can be no doubt of the fact that the sympathetic 

 branches contain filaments capable of modifying the calibre 

 of the blood-vessels, and that the cerebro-spinal nerves also 

 contain elements possessing analogous properties ; but when 

 we reflect upon the extensive anastomoses, in both directions, 

 between the sympathetic and the ordinary motor and sensory 

 nerves, we can appreciate the importance of determining the 

 exact origin and course of these vaso-motor fibres. The first 

 important question is, whether the vaso-motor filaments be 

 derived from the sympathetic ganglia or from the cerebro- 

 spinal centres. 



All experiments upon the question just proposed tend to 



1 MOREAU, Experiences physioloyiques sur Vintestin. Bulletin de Tacademie 

 imp-.riale de medecine, Paris, 1860, tome xxxv., p. 388. 

 8 See page 432. 



