THE BLOODVESSELS IN INFLAMMATION. , 151 
obliterated by constriction, both above and below the point of 
section ; and, as a direct consequence, there is an exsanguine 
state of the part to which the artery leads. In a minute or so, 
dilatation of the artery, both above and below the wound, ensues. 
In the upper part of the artery the flow of blood is re-established, 
as far down as the first considerable branch above the place of 
section. Into the part of the artery below the wound blood 
enters only in a retrograde direction, and that very slowly by 
regurgitation from the capillaries and veins, and in some cases 
from an anastomosing artery. This tardy flow of the blood is 
congestion ; eventually stagnation takes place in the greater 
number of capillaries and venous radicles. “The effect of 
section of an artery of the web of the frog on the flow of blood 
in the part to which the artery leads is thus congestion and 
stagnation, the manifestation of which to the naked eye is a 
reddish spot.” If the artery be divided at some distance from 
the capillaries, then the congestion and stagnation are at some 
distance from the wound. The retardation and ultimate ces- 
sation of the current is due to the removal of vis a ter go. 
2d. — The Effect of Section of a Vein or Veins of the Web of 
the Frog on the Flow of Blood in the Part. — After the section 
of a vein, there is no further flow of blood in the upper segment 
from the wound up to the first considerable branch which enters 
the vessei ; below the section the floyp of blood becomes retro- 
grade to another vein, if there be an anastomosis with such. 
When the latter was also cut, the vein received blood in the 
natural direction by one set of radicles, whilst by another set 
it sent the blood away in a retrograde direction to capillaries, 
from which the blood passed into the radicles of another vein. 
Having thus to pass through two sets of capillaries, congestion 
took place in the capillaries and venous radicles — stagnation in 
a few only. The less disposition to congestion in the capillaries 
after division of a vein than an artery is due to vis a ter go 
being cut off much more completely in the latter than in the 
former case. 
4 th . — The Effect of Section of the Ischiatic Nerve on the Flow 
of Blood in the Web. — After section of this nerve, the arteries 
are rather dilated, and, as a consequence, the flow of blood is, on 
the whole, more rapid, and there is less disposition than in the 
natural state to congestion and stagnation from the action of ex- 
ternal agents. 
6th. The effect of section of arteries, veins, capillaries, and 
nerves, altogether, on the flow of blood in the part, is a com- 
bination of the effects above described. 
Exudation in the case of inflammation from wound of the web, 
