216 BIOLOGY. [Book ii. 



of special nerves, of motory nerves of the vessels, or vaso- 

 motories. The function of the vaso-motory nerves is of such 

 importance that it is indispensable briefly to describe it. 



The vague notion of nerves specially charged to regulate the 

 distribution of blood in the vessels is very old in science. 

 Already even in 1727, Pourfour du Petit had noted the fact 

 which in our own days has led M. Schiff in Germany, and M. 

 01. Bernard in France, to the discovery of the vaso-motory 

 nerves. Whosoever has opened a treatise on anatomy knows 

 that the peripheric parts of the nervous system, situated apart 

 from the nervous column — the nerves, properly so called — are 

 distinguished into two great categories. One of these categories 

 comprehends cords, smooth, cylindrical, and appertains to motility 

 and to sensibility. The other is composed of cords along whose 

 passage enlargements or ganglions are found ; this is the gang- 

 lionary nervous system, which has for a long time been called 

 the symjiathetic nervous system or the system of organic life, 

 because its principal branches are especially distributed to the 

 viscera. We propose to give further on a somewhat less 

 succinct description of the ganglionary nervous system. For 

 the moment we must satisfy ourselves with saying that as a 

 whole it is composed of two chains of ganglions placed on each 

 side of the vertebral column. 



These ganglions, connected with each other by vertical nervous 

 cords, are, on the one hand, united by other nervous branches 

 to the spinal marrow, and send forth numerous branches, 

 distributing themselves to the viscera, penetrating even to all 

 the tissues and organs of the body, and clinging more or less 

 straightly to the arteries. In the cervical region in man, we 

 count three cervical sympathetic ganglions, of which the higher 

 one sends forth fibres which adhere to the intracranian and 

 extracranian arterial branches. Now, as early as 1727, Pourfour 

 du Petit had remarked that the section of the great sympathetic 

 nerve in the neck provoked congestion of the eye and the redness 

 of • the ocular conjunctiva. To think that the cutting of the 



