Again, in the course of Dr. Hastings' inquiry, it is proved that the healthy circulation of the blood essentially depends upon a due degree of action in the vessels throughout the system; that the application of stimuli, whilst it increases the action of the vessels, produces none of the symptoms of inflammation. When, however, the excessive action of these stimuli has impaired the excitability of the small vessels, the phenomena of inflammation are fully manifested, and when their excitability is restored the inflammation subsides. It may be logically inferred, therefore, says this writer, that inflammation consists in a weakened action of the capillaries, by which the equilibrium between the larger and smaller vessels is destroyed, and the latter become distended. And with respect to the conclusion drawn by Dr. Thomson from his experiments, that inflammation in moderate degrees consists of an increased action of the vessels, Dr. Hastings maintains that the writer's belief in the excitement of the capillaries, in some cases of inflammation, arises from his having denominated that a state of inflammation which ought not to be so called. "The application of salt" (says Dr. Thomson) "produced an increased velocity in the dilated larger and smaller arteries and capillary vessels to which it was more immediately applied.

In nine experiments, the phenomena of which I hare minutely recorded, the application of salt was not only followed by a bright red colour visible to the naked eye, and a sensible enlargement of the arterial and venous branches, but with an increased rapidity of circulation in the capillary vessels, the globules becoming less distinct than before the application of salt, and obviously less distinct, from the rapidity of their motion, than the globules in the capillary vessels in the uninflamed part of the frog's web The repeated application of salt was, however, sooner or later followed by retarded capillary circulation, or even by complete stagnation."

Now, with regard to those experiments which seemed to J)r. Thomson to justify the inference that moderate degrees of inflammation may be attended with an increased velocity of the blood in the inflamed vessels, Dr. Hastings, as I have already said, objects that the appearances seen, while such velocity of the circulation presented itself in the vessels affected, ought not to have been denominated inflammation, because it constantly happened in his own experiments that when inflammation commenced, no globules could be seen even in the blood of the affected vessels. It was universally converted into a bright red homogeneous fluid. So that globules could never bo seen in the capillaries of a really inflamed part, much loss moving with great rapidity. He argues that the state alluded to by Dr. Thomson is only that temporary excitement of the capillaries generally preceding their debility, which is inseparable from inflammation.

Another writer asks "whether either of the variations in the state of the capillaries, and in the flow of the blood, which have been described by Dr. Thomson, was accompanied with an effusion of lymph, of pus, or by mortification, which are the usual attendants upon the state of inflammation, and by which the existence of that condition might have been distinctly recognised! To this question" (he says), "as far as I am capable of judging, there appears to be but one answer, which is, that although that state of parts which was induced by the application of salt - namely, retardation and stagnation of the blood - presented the strongest resemblance to inflammation, yet in no one instance did either state continue for a sufficient length of time to allow any one of the usual accompaniments of inflammation being produced, since each variation terminated more or less speedily in the restoration of the natural current."' He maintains that no sign of inflammation can be detected while the velocity of the blood's motion is increased, but that inflammation is immediately recognised when it is retarded, and disappears as the healthy current is restored.

Now for the purpose of demonstrating clearly the effects of irritation it is necessary to procure the frog, the web of which affords a splendid illustration of the circulation. If you now apply an irritant to a given portion of the web, the globules are seen crowding into the capillaries, which are dilated, and which all carry the blood towards the point irritated. This movement is so evident, that one need only place a red-hot needle upon the course of the minute vessel in which the flow of the globules has been distinctly noticed, in order to see them instantly retrograde towards the point irritated. The capillaries around this point dilate, and seem to multiply themselves, because a greater number is perceived on account of the presence of the red blood, which, in colouring them, renders them more visible. The globules arrive, they are crowded together, their motion is retarded, and at length suspended; they revolve upon themselves, and finally remain entirely at rest, this being the stage where complete stagnation takes place. From this it will be clearly and definitely observed that irritation must be looked upon as the primary cause of inflammation, and that the capillary circulation is suspended in the part irritated. But for some distance around, the retardation of the circulation and dilation of the capillaries are plainly seen. A little further off the circulation is more rapid, the capillaries being still dilated, and the globules of the blood less distinct Here, then, is the explanation regarding the increased velocity of the capillary circulation in the immediate vicinity of an inflamed part, and which never ought to be lost sight of, since it clearly shows that more blood may pass through the surrounding channels during the stagnation in the focus of the inflammation, than through the whole part before the stagnation existed.

It therefore appears that all the vessels of an inflamed part are dilated, and that while the motion of the blood is retarded or completely arrested in some, a greater quantity than usual is forced through the others.

I have only another observation to make ere we proceed to the consideration of the symptoms, and that is this: The period of true inflammation is characterised by complete interruption of the circulation: the blood coagulates, clogs the vessels, and stagnates in several points of the inflamed part, due to an increase of fibrine, which fibrine exerts such an all-powerful sway that it draws the blood to itself, holding it by an unseen power; serum then ensues, a change of structure is produced, while the functions of the part are completely suspended. These changes, then, are attended with increase of the swelling, heat, redness, and pain.