326 PHYSIOLOGY. 



erigentes leave the cord by the anterior roots of the first, second and 

 third sacral and go into the hypogastric plexus. The vasodilators of 

 the laryngeal mucous membrane come by the pneumogastric for irrita- 

 tion of the peripheral end of the superior laryngeal makes the mucous 

 membrane red. 



All the facts show that, with the exception of the vasodilators, 

 which flow in the different cranial nerves, the majority of branches are 

 found mixed with the vasoconstrictors in the sympathetic trunks, and 

 the same nerve, like the sciatic, can give vasoconstriction or vaso- 

 dilation. The muscles are mainly supplied with vasodilators. 



The results of irritation of the vasodilators are necessarily 

 opposite to those which result from an irritation of a vasoconstrictor. 

 With vasodilators the blood-pressure falls in the dilated vessel and the 

 veins by the increased flow of blood have an elevation of pressure, the 

 organs supplied by these nerves become red and their volume and 

 temperature increase. 



All vasomotor nerves are distributed to unstriped, involuntary 

 muscles; spinal nerves to striped voluntary muscles. The former are 

 always characterized by being ganglionated ; in other words, possessing 

 cell-stations, or relays, in their course from the central nervous system 

 to the muscular fibers which they govern. 



The vasodilator nerves behave very similarly to the cardiac 

 branches of the vagus, for, when both are stimulated, the result pro- 

 duced is inhibition and relaxation. Nicotine is said to be a powerful 

 excitant of the vasodilators. 



Recognition. It is easy to recognize a vasodilator nerve when 

 it contains no other fibers. But, should it be mixed with vasocon- 

 strictors going to the same organ, it becomes necessary to make spe- 

 cial arrangements. These are occasioned by the fact that the vaso- 

 constrictors usually overcome the dilators. However, the constrictors 

 become tired more quickly, and after they are exhausted the vaso- 

 dilators act. 



By warming or cooling an extremity with water, the experi- 

 menter can, on irritating a nerve, obtain a dilatation or a narrowing 

 of the blood-vessels supplied by it. When in the same nerve two 

 kinds of vasomotors run, then by the same irritation in warming the 

 foot there is obtained a contraction of the vessels, and in the second 

 place a dilatation on cooling the foot. 



Differences in Two Kinds of Nerves. Vasomotor nerves present 

 differences in their actions dependent upon division and degeneration 

 in the same. After degeneration, an irritant to a nerve calls out 



