But it must be remembered that several difficulties remain, upon which experiments throw no light For why does a failure of power of small extent in the capillaries of a vital part strongly excite, not only the larger arteries of the part affected, but those of the whole system, while a more extensive debility of the capillaries of an external part excites less increased action in the larger arteries of that part, and often none at all in those of the system in general?

Why does inflammation often move suddenly from one part to another, when we see no cause either increasing the action of the capillaries of the inflamed part, or weakening those of the part now affected? Why does inflammation often arise in parts only sympathetically affected, and consequently far removed from the offending cause? Why is inflammation often apt to spread to neighbouring parts, between which and the part first affected there is no direct communication of vessels, as to parts in continuation with that part?

Those phenomena, it is evident, are referable to the agency of the nervous system, and seem readily explained by experiments, which prove that the effects of both stimuli and sedatives, acting through the system, are felt by the vessels, and that independently of the intervention of any effect produced by the heart. Thus the irritation of the nerves of an inflamed part may excite the larger arteries of this part, or of distant parts, or of the whole sanguiferous system. It will, of course, be most apt to do so where the irritation excited by the inflammation is greatest, and consequently in the more important vital parts. It cannot appear surprising that inflammation should suddenly cease in one part and attack another, when we know that the nerves are capable of exciting to due action the capillaries of the one part, and in the other of impairing the vigour of those which have not suffered. In the same way we account for parts only sympathetically affected becoming inflamed, and for inflammation readily spreading to neighbouring parts, which always sympathise, although there is no direct communication between them, either of vessels or nerves.

Now in order to reconcile this difference, Dr. Hastings' investigations with the microscope brought him to the following conclusions: "That certain stimuli, applied to living parts, produce an increased velocity of the blood's motion, and a contraction of the blood-vessels. During this state of excitement, the part affected is so far from giving anything like the appearances of inflammation that the size of the vessels is diminished and the part paler. But if the stimulus be long continued, or increased in power, the small vessels which, in the natural state, admit only of one series of globules, become so dilated as to allow an accumulation of a much less fluid and redder blood in them, which loses its globular appearance, and moves much more slowly, than that which previously passed through the vessels; the part now appearing inflamed. If the stimulus be removed, the vessels do not soon regain their original state, time is necessary to allow them to recover their contractile power, so as to prevent the impetus with which the blood is propelled by the heart and larger arteries from keeping up the dilated state of the capillaries. Here then we are obliged to admit with Boerhaave that there is an error loci; for a denser and redder blood passes into small vessels, which much more fluid contents, but the error loci does not cause the inflammation, but results from the previously weakened state of the capillaries. In this manner the blood may occasionally be extravasated in inflammation, without any actual rupture of a vessel, for the exhalents may be so weakened and dilated as to allow globules to pass through them.

If the stimulus which produces the inflammation be of a very acrid nature, debility of the vessels is frequently induced without any previous excitement. The blood in all the smaller vessels becomes very red, circulates very slowly, and in some vessels stagnates.

The application of a stimulus, different from that which produced inflammation, will sometimes bring on resolution. When this occurs the dilated vessels contract; they no longer contain a red, dense, homogeneous fluid, but again receive blood, consisting of small nearly colourless globules, which float in a colourless fluid, and the motion of these globules at length becomes as quick as before the inflammation took place. If, however, the inflammation proceed, the blood becomes nearly stagnant; it continues very red, and the vessels are much dilated.

When this high degree of inflammation is not relieved, sphacelus ensues. The part then feels softer to the finger and gives way with less force. The vessels are much dilated; the blood does not move, it loses its red colour, and becomes of a yellowish-brown hue. The separation of the dead from the living part takes place soon after this change in the colour of the blood. Whilst the ulceration produced by this separation of the dead from the living part of the web is healing, the capillary vessels distributed on the ulcerated surface and the contiguous parts are much distended with arterial red blood, which is moved very slowly. When the ulceration is healed, the vessels become contracted, and circulate the fluid with the same degree of velocity as before the inflammation was excited. With respect to the seat of inflammation, it may be observed that the capillaries are first affected, but even the small arteries of the web are also occasionally distended. (Such were Dr. Hastings' opinions.)

With respect to the doctrine espoused by some authorities, that the smaller branches of veins are the exclusive seat of inflammation, it may be observed that this idea is difficult to solve, for how can we tell whether the arteries or the veins are exclusively affected? Is the distinction even practicable? If we trace the vessels of a part, we soon come to the points at which we can no longer distinguish between arteries and veins; we find a minute network of vascular ramifications, which cannot be unravelled or distinguished.