508 THE NERVOUS SYSTEM. 



striction of the blood-vessels throughout other parts of the body, indi- 

 cated by increased arterial pressure. A similar result is produced by 

 irritation of the trigeminus or other sensitive nerves or nerve roots, 

 or by that of extended regions of the integument. According to Yul- 

 pian,* this effect is very observable, in dogs, on the under surface of 

 the tongue after division of one sciatic nerve. On galvanizing the 

 upper extremity of the nerve, the under surface of the tongue grows 

 paler, and its superficial veins diminish visibly in size, or even become 

 imperceptible. This action, which is first conveyed by the sciatic nerve 

 to the spinal cord, is finally transmitted to the tongue through the 

 fibres of the sympathetic ; since if the sympathetic be divided in the 

 cervical region, the above results are no longer produced on that side 

 from irritation of the sciatic nerve. 



Reflex dilatation of the blood-vessels is also of frequent occurrence. 

 It is distinctly manifested in the rabbit's ear on galvanizing the central 

 extremity of the anterior cervico-auricular nerve after its division. This 

 effect, formerly observed by Schiff and Rouget, is, according to Yulpian, 

 one of the easiest to reproduce ; especially if the animal be first poisoned 

 by woorara, which suspends the action of the voluntary muscles, and 

 prevents their interfering with the blood-vessels by local contraction. 

 Reflex vascular dilatation is also the usual accompaniment of local 

 injuries or irritations. Congestion soon shows itself in the neighbor- 

 hood of any wound in the integument or subcutaneous tissues ; and the 

 intestines, when exposed by opening the abdominal cavity, become 

 rapidly covered with an increased vascularity. 



The most familiar examples of reflex dilatation are those occurring 

 in the glands and mucous membranes at the time of their functional 

 excitement. These organs present alternate conditions of repose and 

 activity. In the former condition their blood-vessels are moderately 

 contracted, supplying blood in small quantity for the nutrition of the 

 glandular tissues, or for the preparation of their special organic ingre- 

 dients. But when the period arrives for active secretion, there is a 

 dilatation of the blood-vessels, with increased local circulation and free 

 exudation of the secreted fluids. This phenomenon was witnessed in 

 the mucous membrane of the stomach, so long ago as in the obser- 

 vations of Beaumont* on the gastric fistula of. Alexis St. Martin ; and 

 it has subsequently been observed in many similar cases. In the sub- 

 maxillary gland of the dog, reflex vascular congestion is at once pro- 

 duced by introducing vinegar into the mouth, or by any stimulus 

 which excites the salivary secretion. A similar variation was found 

 by Bernard in the vascularity of the pancreas and duodenum, in the 

 dog, under the conditions of fasting and digestion. In the intervals 

 of digestion these organs are pallid, with but few blood-vessels visible 

 upon their surface. But after the introduction of food, and while 

 digestion is going on, their appearance is greatly changed. The 



* Lepons sur 1'Appareil Vasomoteur. Paris, 1875, tome i., p. 238. 



f Experiments and Observations upon the Gastric Juice. Boston, 1834. 



