endowment of the vascular membranes, and only capable of being affected by the action of the nerves, as well as by direct stimulus. The effect of an atonic state of the walls of the vessels is well illustrated by an experiment performed by Dr. Williams: he adapted to a syringe a tube with two arms, one of which was connected with a metal tube, and the other with a portion of dog's intestine, of the same length as the metal tube, but, when distended, double its diameter. Water was now thrown in by the syringe, and the quantity discharged from the open ends of each of the two tubes estimated. The metal tube in the same time yielded three times more liquid than the intestine. Now a vessel, whose wall is possessed of a proper degree of contractility, may be compared to the metal tube. The force of the heart communicated by the fluid to its walls is not lost, but reacts again immediately upon the fluid and drives it onward. The vessel, with atonic flaccid walls, resembles the intestine, which yielded to the distending force of the column of fluid, and, from not reacting upon it, allowed a great part of the force to be lost as an impelling influence.

The effects of congestion have already been partially noticed. They have reference mainly to two circumstances: one, the impairment of the vital actions of the part, the other, the effusion from the overloaded vessels of watery, albuminous, or mucous fluids. When the arm is tied up for venesection, a sensation of numbness, weakness, and chilliness, is felt after a time, showing that the sensibility and contractility of the limb are impaired by the congestion which has taken place. In the hepatic and renal congestions, which often are produced by obstructive disease of the heart, the secretion of bile and of urine is commonly diminished, or morbidly affected. Cerebral congestion interferes materially with the free exercise of the functions of which the brain is the instrument. This impairment of vital (i. e. special) power depends partly on the more increased quantity of blood in the part, which, being greater than is proportionate to its functional activity, overloads and oppresses it. If it be true-as we shall see reason to think that it isthat the supply of blood to a part is, in a measure, dependent on the vigor and energy of life which that part possesses, it will not be difficult to conceive that an over-supply of blood will have an injurious and depressing effect on the same vital powers. But a still more powerful, and quite unquestionable, cause of vital depression in a congested part, is afforded by the altered condition of the blood itself, which, semi-stagnating in the capillaries and veins, becomes more venous than it should, and otherwise unfit for the healthy nutrition of the tissues. The sloughing ulcers which form in the congested and thickened integuments of the lower limbs, when the veins are enlarged and varicose, are a striking instance of the lowered condition of the vitality of those textures. Longcontinued congestion of the liver, from disease of the heart, produces a very remarkable effect on the parenchymal cells. They become very greatly loaded with yellow matter (which does not appear to be true biliary, but rather bile pigment); in extreme cases, the majority atrophy, and are reduced to a mere granular detritus, while the capillary intercell-spaces become enlarged. These changes afford some explanation why the secretion of bile is interfered with, and also why jaundice

occurs. The effusions that take place from congested parts are certainly the most prominent phenomena of the condition. They will be most abundant, as a general rule, when the congestion depends on venous obstruction; so that, while fresh blood is being poured into the part, no exit can be found for it, except that which the exudation affords. They may also be extremely abundant in some cases, in which not only the tonicity of the vessels is entirely lost, but the texture of their walls is altered, so that they no longer oppose any obstacle to the escape of their contents, but allow them (the fluid part) to transude with great facility. Such is, no doubt, the case in instances of bronchorrhoea, chronic diarrhoea, and leucorrhoea, where large quantities of fluid are continually passing off from the toneless vessels, but where no venous obstruction exists, or none that is commensurate to account for the discharge. The effect of remedies in these cases shows that the discharge is dependent on the cause we have mentioned. Under the administration of turpentine or astringents the vessels regain their tone, and no longer pour out their contents. Though the vascular atony may in such states have originated in congestion, yet as this is removed by the effusion while the atony remains, they come at last to be rather instances of passive flux, or dropsy. Chronic ascites, in which the smaller branches of the portal vein may be so obstructed that no fluid can pass through them, presents an exquisite instance of effusion depending upon venous obstruction. The fluid effused in the peritoneal sac varies a good deal, chiefly as to the relative proportions of water and albumen which it contains. In the table subjoined at page 116, one instance is seen in which the water amounts to 988 per 1000, and the albumen to only 0.9, while in another the water does not exceed 704, and the albumen is in the prodigious quantity of 290. Not only does a more or less watery serum exude, but fibrin not unfrequently accompanies it. Large flaky masses of fibrinous coagula are not uncommonly found in the peritoneal cavity after death in cases of ascites, and the same are also seen occasionally in the fluid evacuated by paracentesis. We have also seen blood-globules so uniformly dispersed through the fluid, that there could be no doubt that they had escaped from the congested sub-serous capillaries, and were not accidentally mingled with the effusion. The same products of congestion also occur in the urine when obstructive disease. of the heart throws back the blood on the veins. The secretion is albuminous, contains fibrinous casts of the tubes and blood-globules. Decided hemorrhage may also occur, as the result of extreme congestion, which may be dependent either upon venous obstruction or upon an atonic state of the vessels. Melana, or hemorrhage from the bowels, is an instance of the first, passive menorrhagia and epistaxis, of the latter.

It

We shall return to the consideration of effusions proceeding from congestion, when we speak of the results of hyperæmia generally. is a remarkable and instructive fact, that congestion of parts never seems to occasion hypertrophy; or, if this should appear to have taken place, closer examination proves that rather the reverse is the case; that the hypertrophy is what Rokitansky calls unreal. Thus, a large bacony spleen or liver may appear to be hypertrophied; but the in

crease in size is not due to the formation of fresh natural tissue, but to the infiltration and addition of an unnatural product, among which the real structure is found atrophied. In these particular instances the deposits may not have proceeded from congestion; but they afford an exact illustration of what often takes place in congestion in a less degree. It seems also very doubtful whether simple passive hyperæmia, as such, does produce even these unreal hypertrophies, or whether in all such instances the crasis of the blood is not also altered in some special manner. After very numerous examinations of congested livers from persons dying with heart disease, we have not been able to convince ourselves that the hyperæmia gives rise to any new product, or that it is an exciting cause of the cirrhotic alteration which may also exist. We have already pointed out the impairment of vital power which congestion occasions, and the causes inducing it, which seem to afford an adequate explanation of the non-tendency to growth and development which is observed both in the affected part itself and in its interstitial effusions. The following sentence from Mr. Simon's lecture recognizes and similarly explains the same fact: "It is true, that much blood is contained in the affected tissue; but it is blood that has insufficient means of renewing itself; and from its long detention in the part it acquires, in an extreme degree, the character of venous blood. Thus, as regards mere bulk of blood, the part is over-supplied, but, in respect of the quality of blood, it may be said to suffer what is equivalent to anæmia: accordingly, the elements of its texture fall into a state of atrophic softening, which terminates in the formation of an ulcer. I think it not improbable that the same fact may contribute to explain the continued non-development of those effusions which arise from passive hyperæmia.' It thus appears that atrophy, rather than hypertrophy, is likely to be the result of abiding congestion of any part.

The effects of congestion of a part, especially if it be one of some magnitude, may not be confined to the part itself, but may affect the system generally. This appears in two respects, one being a degree of faintness and depression, occasioned by the withdrawal of a considerable quantity of blood, from active circulation; the other, an injurious influence exercised on the whole blood mass by the deteriorated portion, which slowly and partially returns into it again from the seat of congestion. It is clear that an excess of blood poured into one part, and detained there, must leave others imperfectly supplied; the local hyperæmia, according to its extent, produces a degree of general anæmia. That blood which has long been stagnant in a part must be in an unhealthy state is very comprehensible, and that, by its mingling with the general mass of blood, deterioration of the same will be induced, and therewith a cachectic state. Thus, when a congested state of liver exists, there are, frequently, abundant lithates present in the urine; the blood, returning from the liver, conveys into the circulation matters which induce an unnatural state of the renal secretion and more or less of general disorder.

ACTIVE HYPEREMIA.-DETERMINATION OF BLOOD.

This is the second variety of local hyperemia that we have to consider. The general phenomena of this condition are manifestly different from those of passive hyperæmia, and convey the idea of increased activity and vigor in the vital process. The flow of blood to the part is increased; the capillaries, without being greatly distended, are well filled, and give a more or less suffused red blush to the face, very different from the duller tint of congestion. In consequence of this filling of the capillary plexus, and, perhaps, also of some slightly increased blastemal exudation, the turgescence of the part is increased, and its temperature elevated. The arteries leading to the seat of active hyperæmia often pulsate with more than ordinary force, so as to have given rise to the idea and term of "increased vascular action." They must also be enlarged to admit the greater quantity of blood that the part receives, and this enlargement becomes permanent; that is to say, the whole vessel assumes larger dimensions, when the hyperæmia is a healthy and natural state. The veins also enlarge, but are not distended as they are in congestion. The sensibility of the part is commonly increased; its function may be, or may not, and the same is true of its growth.

This brings us to the inquiry, whether active hyperemia may not be distinguished into two forms, one to be regarded as healthy, associated with increased vital power and capacity for action; the other morbid, attending upon and promoting unnatural action, resulting in disease and decay. There are many well-known and oft-quoted examples of healthy hyperæmia, such as the female breasts during gestation and lactation, the uterus during the period of pregnancy, the gums during dentition, the mucous membrane of the stomach while the secretion of gastric juice is going on, and, generally, it may be said, every organ during the time of increased activity and employment. Now, we think it may be affirmed, that, in the above instances, the most important and characteristic phenomenon is the increased functional energy and vigor of the hyperemic part; this we believe to be the main and essential circumstance of which the increased blood-flow is a sequel. Nay, there are many instances, especially among secretory organs, in which the great increase of the product proves that a corresponding increase of the supply of blood must have taken place; a true hyperæmia, in one sense, exists, but it is not apparent, because of the active transformation which is going on. How marked is the difference between this condition and congestion! In the one, functional activity and molecular change at its height, with vascular injection more or less considerable, but not varying in direct, rather in inverse, ratio to it; in the other, vascular injection extreme, while the functional activity is extremely depressed. Now, in proportion as active hyperemia departs from the physiological condition and becomes morbid-that is to say, approaches towards inflammation-in the same degree does the vital energy and activity of the part appear to be lowered, and the hyperæmia becomes the more marked phenomenon. Thus, a diuretic drug shall be administered to two individuals: in the one, the flow of urine

shall be considerably augmented, the vital power of the kidney predominating over the hyperemia excited; in the other, the flow of urine shall be diminished, and the secretion become bloody and albuminous, evidencing the predominance of the hyperemia over the vital power. So, too, in fever. The skin, at one time, shall be dry, and burning, and red, with vascular injection, but its vital power of secretion and exhalation is in abeyance. But a change comes, the tissue regains its functions, and pours out a healthy moisture on the surface; and now the hyperæmia, though it may continue in some degree, is no longer predominant. How different must be the condition of the gastric mucous membrane in the hyperemia excited by a few grains of ginger, and that produced by a few grains of arsenic! No doubt the one form of active hyperæmia may pass into the other. The quantity of blood which a healthy tissue was able to employ, and which was requisite for the unusually vigorous discharge of its function, may become too much for the same tissue when debilitated by over-use. A brain ministering to an active mind, requires and receives a greater supply of blood than that of the waterman "who rows along thinking of nothing at all." So long as the cerebral energy is not overtasked, the hyperemia will tend to no injurious result, but will only supply the necessary pabulum for the material changes connected with thought. When, however, the time arrives that the delicate organ needs repose, then if the strain be continued, and the hyperæmia kept up, it is manifest that a morbid state will soon supervene, in which the hyperæmia may yet further increase, and the natural energy be still more diminished, till, together with symptoms of disordered and erring action, inflammation, or some other result of hyperæmia, occurs. The phenomena we have alluded to are of every-day occurrence. No doubt can exist about their reality, though different opinions may be entertained as to how they should be interpreted. We shall immediately proceed to consider more closely the different views that have been advanced, but we would ask especial attention to this point which we have dwelt on, viz: that in one form of active hyperæmia, the vigor of the tissues for vital action is increased, while, in the other, it is diminished. In the one the hyperæmia supplies a want, in the other imposes a burden.

Now, before we enter on the consideration of the mode in which active hyperæmia is brought about, let us refer shortly to one or two physiological points, which must form the very basis of all our attempts at explanation of the phenomena. All tissues may be regarded as consisting of vessels, nerves, and the proper elements of the tissue. The vessels, it is true, may be more or less closely woven up with the tissue, or even may not actually penetrate it, but still they are essential. The nerves convey an influence which may affect the blood vessels or the tissue. The elements of the tissue, be they cells, or originally derived from cells, have certain special endowments, which, when called into action, increase the flow of blood to the part; at least, this seems only another form of putting the undoubted fact-that exercise of a part causes more blood to flow thither. The blood vessels consist of arteries, capillaries, and veins. The arteries have a truly contractile coat, which, under some kinds of stimulation, may even produce obliteration