The crassamentum of arterial as well as of venous blood has frequently been observed to exhibit a buffy coat. It is rarely seen in blood extracted by cupping-glasses, and never in that pressed from leeches. It occurs in the lower animals, and is observed as frequently in the horse as in the human subject ; indeed, from the quantity of blood usually drawn from that animal, it is still more strikingly apparent, being occasionally several, inches thick. It has been denied that the cupped appearance is ever met with in the blood of the horse ; but if this be received into a sufficiently small vessel, it will be in some instances as complete as in blood taken from the human subject. There are va rieties in the appearance of the buffed coat which it is worth while to notice. It is gene rally of a firm uniform consistence, and of a light yellow or buff colour, whence its name. Sometimes, however, it is of a more spongy texture, and of a white or bluish, and more transparent hue. Two layers of buff are occa sionally seen ; the upper soft or friable, the in ferior more compact. "There is a difference," says Sir Gilbert Blane, " in the appearance of the blood when sizy, perhaps not sufficiently insisted on by practical writers ; for though there should even be a very thick buff, yet if the surface is flat, and the crassamentum tender, nogreat inflammation is indicated in com parison of that state of the blood wherein the surface is cupped, the crassamentum contracted so as to form the appearance of -a large pro portion of serum, and where it feels firm and tenacious, though perhaps but thinly covered with buff." From the examination of several specimens of buffed blood, I was at one time led to be lieve that its serum was always deficient in its due proportion of albumen ; but this I have since found not to be the case, having met with blood thickly buffed, the serum of which at 60° Fahr. had a specific gravity of only 1.024, and with another specimen where the layer of fibrine was equally thick, of which, at the same temperature, the serum had a spe cific gravity of 1.040. Dr. John Davy examined the specific gravity of buffed blood in eleven cases. In five of them in which the buffy coat was slight, the specific graVities were 1.047, 1.051, 1.054, 1.055, 1.054 ; in five others in which the buffy coat was moderately thick, the specific gravities were 1.044, 1'038, 1'052, 1.056; and in one instance in which it was thick, the specific gravity was 1.057. Taking the mean gravity of healthy blood at 1.044, which I believe will be found correct, it would thus appear that the buffy coat is more frequent in blood above than below the mean weight; but it is also clear that it may exist in either state, and the number of experiments is not sufficient to lead to any conclusive result.
De Haen, Hewson, and others have met with cavities in the crassamentum of buffed blood containing clear fluid (liquor sanguinis), which, on being evacuated several hours afterwards, separated into fibrine and serum. This fact is analogous to that of fluid blood having been found by Hewson in the heart of a dog thirteen hours after death, which blood, on being re moved, coagulated soon after exposure to the air. A similar coagulation will occasionally take place in fluid blood taken from the human heart several hours after the extinction of life.
The remote cause on which the occurrence of the buffy coat depends appears to be an increased action in the circulating system, de pendent on increased nervous energy, and this is capable of being very speedily excited. Thus it has happened* that blood from the same orifice drawn into four cups has exhibited this appearance in the second or the third cup, and not in the first or last, the difference being plainly owing to a faintness felt at the com mencement and termination of the venesection.
Thus also the blood of healthy horses drawn immediately after a smart gallop while the cir culation is powerful and rapid, will exhibit a buffy coat, while that previously abstracted will of course skew no such appearance. Scudamore, it is true, arrived at an opposite result in the case of a young man whom he bled, and after causing him to run two miles, bled again. Neither before nor after the race was the blood buffed, but it is obvious that such severe exercise after depletion would exhaust rather than augment the powers of the nervous and circulating systems. Accordingly he found the proportion of fibrine diminished in the blood last drawn, while the specific gravity of the serum was increased from 1.030 to 1.035, thus shewing how large a quantity of moisture must have been carried off by perspiration. • The buffy coat, as might be anticipated from its cause, is usually found in connexion with those diseases and even conditions of health in which vascular action is preternaturally increased—in the active stages of peripneu mony, in pleurisy, in inflammatory fever, scar latina and the eruptive diseases generally, and very uniformly in acute rheumatism. It is also occasionally but not always met with in the blood of pregnant women, in persons of sanguine temperament and full habit, and those who resort to frequent bloodletting; in chronic rheumatism, gout, enlargement of the heart, and other affections where no inflammation exists. On the other hand, it may be absent even in the most intense inflammation; for the circulation may be so overcharged either actually or relatively, or the nervous power so oppressed, that the requisite degree of propul sive force is not exerted by the heart and arteries, nor the vital energy on which slow coagulation depends imparted to the blood. In such instances the buffed coat generally appears on a second or third repetition of venesection.
Louis found the blood covered by a firm thick buff at each bleeding in nineteen cases of fatal peripneumony out of twenty-four. In two-fifths it was cupped. In fifty-one out of fifty-seven cases of recovery the blood was buffed, and in twenty-three cupped. In nine tenths of rheumatic patients the buff was firm and thick.
The form of the receiving vessel, the degree of motion to which it is subjected, and the size of the orifice in the vein, materially in fluence the phenomenon. M. Belhomme, the experimenter under M. Recamier, has made about one hundred and fifty experiments on blood drawn in health and disease. He has come to the conclusion that a medium orifice one line in the vein, a strong, rapid, and continuous jet in the form of an arch, and a narrow vessel for the reception of the blood, are the external circumstances most favourable for producing the buffy coat.* Fibrine is more abundant in buffed than in healthy blood. Dr. Davy, from his observa tions, infers that there is no constant relation between the appearance of this covering and the proportion of fibrine in the crassamentum, yet his own tabular report contradicts him. " From all the examinations we have made," says Thackrah, who has made many experiments to determine this point, " I infer without hesita tion that buffed blood contains a considerably greater proportion of fibrine than healthy blood." This is a fact of much interest and importance, for as very slight and sudden causes may give rise to the formation of a buffed coat, we are thence led to infer that the quantity of insoluble matter which separates from liquor sanguinis by coagulation is variable, and that there is so far reason to believe that fibrine and albumen are principles convertible into each other.