THE CIRCULATION OF THE BLOOD. 329 



The vaso-constrictors for the viscera of the abdominal cavity pass 

 by way of the splanchnic nerves directly into the collateral ganglia, 

 the semilunar, the superior mesenteric, the inferior mesenteric, and 

 the sacral. From these ganglia an elaborate network of non-medul- 

 lated fibers passes to the blood-vessels of the stomach, intestines, and 

 other viscera, t The great splanchnic nerve is one of the most im- \ 

 portant vaso-constrictor trunks of the body, on account of the large 

 vascular area it controls.// 



The existence, course, distribution, and functions of the vaso- 

 constrictor nerves have been determined by a variety of methods, 

 physiologic and anatomic. Stimulation of the nerve-trunks under 

 appropriate conditions gives rise to a contraction, division to a dilata- 

 tion of the blood-vessels. The physiologic continuity of the pre- 

 ganglionic fibers with the nerve-cells of the sympathetic ganglia 

 has been shown by the intra- vascular injection or the local applica- 

 tion of nicotin. This agent, as shown by Langley, has a selective 

 action on the arborizations of the pre-ganglionic fibers, and when 

 given in sufficient doses suspends their conductivity; hence stimu- 

 lation of the pre-ganglionic fibers is without effect, though stimulation 

 of the post-ganglionic fibers is followed by the usual contraction. 



The following will serve as illustrations of the functions of vaso- 

 constrictor nerves. Division of the great splanchnic is followed by 

 a marked dilatation of the blood-vessels of the intestinal tract ; stimu- 

 lation of the peripheral end by their contraction. Division of the 

 cervical cord of the sympathetic is followed by dilatation of the blood- 

 vessels of the side of the head; stimulation of the peripheral end by 

 their contraction. 



The vaso-dilatator nerves have their origin for the most part in 

 nerve-cells situated in the region of the spinal cord included between 

 the origins of the second dorsal to the second lumbar nerves inclusive, 

 though they are not confined to this region. Some vaso-dilatator 

 fibers have their origin in the medulla oblongata, others in the sacral 

 region of the spinal cord. 



The general course of the dilatator fibers for the intestinal tract 

 is the same as that of the vaso-constrictors, though instead of becom- 

 ing related to the nerve-cells in the pre-vertebral ganglia, they pass 

 by way of the splanchnics to the collateral ganglia, the semilunar, 

 the superior and inferior mesenteric, and perhaps to peripheral 

 ganglia in or near the blood-vessels themselves. 



The vaso- dilatators for the limbs are found in the common nerve- 

 trunks associated with the usual motor and sensory fibers, though the 

 exact route by which they pass from the spinal cord to the peripheral 

 nerves has not in all cases been determined. Their cell stations have 

 not been definitely located. The vaso-dilatator nerves for the blood- 

 vessels of the submaxillary gland arise in the medulla, pass outward 



