63 
j 'probable Action in Health and Disease. 
calibre of the latter vessels, and therefore the quantity of blood 
traversing these and the capillaries, is governed by nerves. 
Now it will be noticed in a flea-bite or other inflammation of 
skin that there is a certain blush which is very deep in colour 
immediately around the wound, but extends a considerable distance 
beyond the point actually injured. This inflammatory blush too, 
as can be easily proved, may be completely removed by pressure. 
If I press the skin, the tint of the inflamed portion will become of 
precisely the same hue as that of the surrounding healthy skin; the 
whole is perfectly pale. When I withdraw the pressure, and the 
blood is permitted to return, the capillaries of the normal skin are 
distended to precisely the same calibre as before, and the dilated 
vessels in the seat of inflammation are again dilated, and to the 
same degree as before the blood was pressed from them. This 
simple experiment proves not only that there exists some mechanism 
by which the calibre of the vessels may be not only increased and 
reduced so as to allow a larger or smaller quantity of blood to flow 
through the capillaries in a given time, but that the increased 
quantity of blood which flows through these tubes in inflammation 
is fixed and regulated by the degree of contraction of the muscular 
fibre cells of the small arteries. This can be determined only 
through the instrumentality of nerves and nerve centres in which a 
certain temporary change has been established and is maintained 
for a time. Such an arrangement as that described in page 59 
would enable us to explain the facts above referred to. 
In the early stages of inflammation probably more blood actu- 
ally flows through the capillaries of the inflamed part than through 
those of the healthy tissues ; but after a time, as is well known, the 
circulation becomes slower, the capillaries are distended, and at last 
the blood ceases to flow. The self-regulating mechanism fails to 
act, and, unless relief speedily follows, may be destroyed. 
Inflammation, as it occurs in the tissues of the higher animals, 
is an exceedingly complex process, in which vessels, nerves, and 
many other structures take part. But other changes are occurring 
during inflammation which produce an influence upon the nerve fibres 
outside the capillary vessels though less directly. If the inflam- 
matory change is not quickly succeeded by a return to the normal 
state, partial or complete paralysis of the little arteries results ; the 
capillaries necessarily become distended, and their walls so attenu- 
ated, that the passage of fluids through them from the blood is very 
much facilitated. There is increased exudation. Now the exu- 
dation that escapes is not simply a clear fluid from which particles 
are deposited after the manner of crystals, and aggregated so as to 
form *'• cells,” but at the time it is poured out there are suspended 
in it numerous living particles. These particles are found in con- 
siderable number, and are probably composed of matter like that 
