590 THE SYMPATHETIC SYSTEM. 



The vascular congestion thus produced by division of the sympathetic 

 nerve is accompanied by three important phenomena, all intimately con- 

 nected with each other. 



First, the quantity of blood circulating in the part is increased, and 

 its movement accelerated. It is not a state of passive congestion ; but 

 all the vessels are simultaneously dilated, a larger quantity of blood 

 passes through the capillaries in a given time, and returns by the veins 

 in greater abundance than before. 



Secondly, there is a remarkable elevation of temperature in the affect- 

 ed part. This elevation of temperature is very perceptible to the touch, 

 both in the ear and in the integument of the corresponding side of the 

 head. Measured by the thermometer, it has been found by Bernard to 

 reach, in some cases, 4.5 or 5 degrees (8 or 9 F.). It results from 

 the increased quantity of blood circulating in the vessels ; since the 

 blood coming from the interior and warmer parts of the body supplies 

 more heat, in proportion to the abundance and rapidity with which it 

 traverses the vascular tissues. 



Thirdly, the color of the venous blood becomes brighter. This effect 

 is also due to increased rapidity of the circulation. The blood is de- 

 prived of its oxygen and darkened in color by the changes of nutrition 

 which take place in the tissues. But if the rapidity of the circulation 

 be suddenly increased, a certain proportion of the blood escapes deoxi- 

 dation, and its change in color, from arterial to venous, is incomplete. 

 The blood accordingly returns by the veins of the affected part in greater 

 abundance, of a higher temperature, and of a more ruddy color, than in 

 the corresponding parts on the opposite side. 



When a local vascular congestion has thus been produced by divi- 

 sion of the sympathetic nerve, if that portion of the divided nerve 

 which remains in connection with the tissues be galvanized, all the above 

 effects rapidly disappear ; the bloodvessels of the ear and corresponding 

 side of the head contract to their previous dimensions, the quantity of 

 blood circulating through the tissues is diminished, the temperature is 

 reduced in a corresponding degree, and the blood in the veins returns 

 to its ordinary dark color. The variations in the rapidity of the circu- 

 lation, dependent on the condition of the sympathetic nerve, have been 

 shown by Bernard' in the following manner. In a living rabbit the upper 

 part of one ear is cut off with a pair of very sharp scissors, so that the blood 

 may escape in jets from the divided ends of the small arteries. The 

 force and height of the arterial jets having been observed, the sym- 

 pathetic nerve is then divided in the middle of the neck on the corre- 

 sponding side Immediately the blood escapes from the wounded ear in 

 greater abundance, and the arterial jets rise to double or even triple 

 their former height. The galvanic current is then applied to the di- 

 vided extremity of the sympathetic, above the point of section, when the 

 streams of blood escaping from the wound diminish or disappear ; but 



1 Journal de la Physiologie de 1'Uomme et des Animaux. Paris, 1862, p. 397. 



