6 INFLAMMATION. 



produces Increased activity of the capillary circulation in the 

 part in which the nerve originates ; and finally, that all arteries 

 manifest alternating states of contraction and dilatation — move- 

 ments independent of those of the heart, and of breathing — and 

 ceasing when the vessels are paralyzed by division of their nerves. 



Eeference to the effect of croton oil shows that acceleration 

 of the flow of the blood through the vessels of the irritated 

 part is sometimes associated with widening, sometimes with 

 narrowing of the arteries; and in order to judge whether the 

 acceleration in the one condition is of a similar or of an opposite 

 nature to what it is in the other, investigators have observed 

 both conditions simultaneously in the same part. If, for 

 example, in the web of the frog's foot the acceleration due to 

 electrical excitation of the central end of the sciatic nerve is of the 

 same nature as inflammation, we should expect it to be increased 

 by local irritation ; and, conversely, the effect of irritation, if 

 already existing, to be heightened by exciting the nerve. The very 

 careful experiments of Dr. Eiegel show tliat it is so. Having 

 found that atter section of the sciatic nerve the effects of irritation 

 were slightly retarded, but otherwise unmodified, he repeated the 

 observation in another animal, excited the central end, and then 

 applied croton oil to both webs. On the injured side the 

 accelerating effect of the croton oil lasted much longer than on 

 the other, so that at the time stasis had already set in on the 

 sound side, the circulation was going on more briskly than 

 natural on the injured side. — (Burdon Sanderson.) 



From the foregoing observations, the reader will gather that 

 acceleration of the flow of blood through the part is the only 

 constant fact observable, whether the cause be the reflex electrical 

 stimulation of a nerve, or the direct irritation of the part by 

 agents which induce either contraction or dilatation. 



In all forms of inflammation of sufficient intensity, the circu- 

 lation, after a varying period of excitation, becomes retarded. 

 The current then ceases, the vessels at the same time become 

 greatly distended, and the blood globules adherent to certain 

 parts of the sides of the vessels, and to each other, so that 

 their individual forms can no longer be distinguished. In some 

 cases the vessels have fusiform dilatations of their whole 

 circumference at certain points of their course, or at short 

 intervals pouches sprout from the sides of their walls. These 



