the blood as to examine a body, it is certainly to be desired that he should be enabled to read, in the physical appearance of the blood he removes from a patient, those constant characters, that more or less clearly reveal its intimate composition, and to which they have been shown to bear a necessary relation. The labours of Prout, Denis, Lecanu, Andral, and Gavarret have revealed to us so many facts that, although the pathological doctrine of the blood is not quite complete, the morbid anatomy of this fluid portion of the organism stands upon an equality with that of its solid tissues."-Vol. 106, p. 76.

1. On the Influence exerted by the Coagulability of the Blood in the production of the Buffy Coat.-Every one knows that blood drawn from the arm separates in very different periods of time into clot and serum; and the question here agitated is what effect has its more speedy or tardy coagulation in the induction of the buffy coat. Some experiments of Hewson upon this subject, as we have already stated, attracted the author's attention at an early period; and these, with some observations he had the opportunity of making in the hospital, led him to the opinion that a slow coagulation of the blood was highly favourable to the production of the buffy coat. So many chemists of celebrity however support, and so many oppose this opinion, that he deemed it an excellent occasion for instituting a series of experiments, which, from their number and the care with which they were conducted, would be in a position to secure acquiescence in the results they indicated.

It is obvious, in a question of time of this sort, unless great care be taken in ascertaining the precise period of coagulation, great errors may easily occur. The following is Signor Polli's criterion.

"The blood was caught in a conical glass vessel holding about an ounce, and which when nearly filled was left in a state of complete rest. Watch in hand, the instant of complete coagulation was carefully observed. The criterion of this was the witnessing a few drops of serum transude at the surface of the consolidated coagulum or between the edge of the crassamentum and the parietes of the recipient. The point at which the blood ceases to be fluid, and solidifies, so that the recipient may be turned upside down without pouring it out, did not seem to me to be so true a point for determining the existence of complete coagulation, as that derived from the transudation of a few drops of the serum, which is to remain permanently fluid, through some portion of the consolidated mass. This fluid, if collected and placed in a watch-glass, remains constantly fluid, undergoing no manner of coagulation. As long as the serum continues imprisoned within the tissue of the clot, rendered more or less dense by its commencing coagulation, we cannot say that such coagulation has taken place; but when the serum is beginning to separate itself from that which was only maintained fluid by the vital influence, and which has now passed into the solid state, the fact is decided."-Vol. 106, p. 86.

The “ fixed point" here indicated is of unquestionable importance, since, without the aid of some such test of complete coagulation, different observers will infer this to have taken place at very different periods. Dr. Polli adds that, it very seldom happens that the serum does not then show itself; but still occasionally the coagulum contracts adhesion with the recipient sufficiently firmly to prevent its passage. By gently moving the edge of the coagulum by means of a feather, or even inclining the vessel on one side, the serum is rendered apparent. Blood so observed has led the author to lay down the three following propositions.

1817] Dependence of the Buffy Coat on slow Coagulation. 305

(A.) That blood forming a buffy coat takes a much longer space of time to coagulate than does blood which forms no such coat.-The blood examined in 405 cases of disease, was found to have required the mean period of 27 min. 30 sec., when it produced the buffy coat, and but 11 m. 50 s. when no buffy coat presented itself—that is to say, a period much less than a half in the one case than in the other. The time required for blood to coagulate, when this was buffy, was found to be nearly twice as long in the case of men (41 m.) as in that of women (23 m.); and that this last generally takes a notably longer time to coagulate than does that of children (18 m.). The cases were taken as they presented themselves without selection in the hospital.

(B.) Blood which of itself would not produce the buffy coat, presents this whenever its coagulation can be sufficiently delayed.-Alkaline solutions, employed not in sufficiently strong proportions to maintain the permanent fluidity of the blood, possess the power of retarding its coagulation; and in twenty experiments here referred to, portions of blood, which otherwise gave no buff, were in this way delayed in their coagulation for some hours with the effect of inducing a buffy coat. In like manner, normal blood may be made to produce this by delaying its coagulation through the prevention of the contact of air by a layer of oil or carbonic acid gas.

(c.) Blood disposed to produce a buffy coat may be prevented doing so by sufficiently accelerating its coagulation.-An experiment repeatedly performed by the author conclusively settles this point. Let blood from the arm of a patient suffering from inflammation be caught in two separate vessels, one of which is to be put aside at once, and the contents of the other previously stirred for a minute or two by the finger or a glass rod, or the vessel so shaken as to keep them in motion for that time. It is then to be set aside also. The first portion will complete its coagulation in 25, 30, or more minutes, giving a more or less thick buffy coat, but that which has been agitated will coagulate in ten minutes, presenting no buffiness whatever: so that persons who have been shown the two coagula could hardly credit they were produced from the same blood, being disposed to consider the one a specimen of morbid, the other of normal blood. Other means of accelerating coagulation, such as adding water to the blood as it flows from the vein, or maintaining it at the same temperature as it had held in the body, produce the same result. The same thing may indeed be observed oftentimes naturally as well as artificially. Thus, during a venesection, the first blood abstracted coagulates slowly and buffs, while the latter portion coagulates far more rapidly and without the buffy coat. So, too, if we abstract blood from both arms, one of which has been maintained turgid by the application of the fillet some time before, and which has only been applied to the other just before opening the vein in the former case the blood coagulates rapidly without buff; in the latter, slowly and with the amount of buff usually observed in the particular disease.

2. Of the Accidental Circumstances which are capable of modifying the Appearance of the Buffy Coat of the Blood.-The examination of these may lead us to the explanation of the various apparent exceptions to the law laid down. The circumstances which may give rise to variations in the manifestation of the effects dependent upon the coagulation of the

blood may be divided into such as are intrinsic and such as are extrinsic to the blood. The first are the density and temperature of the blood when it quits the vein: and the second, embrace the contact of the atmospheric air, the nature of the recipient, the temperature of the air, the agitation the blood is submitted to, and the rapidity with which it flows.

(1.) Density of the Blood.-For the estimation of the density of the blood Dr. Polli employs an areometer which is divided into ten degrees an inch apart, each degree being subdivided into ten parts. The density of the blood, in reference to its buffy or non-buffy state, was examined in 180 instances with the following general results.

"That a lesser density accompanies buffy blood, as a greater density is associated with unbuffed blood; since, taking it generally, the density of the buffed is to that of the unbuffed blood as 5'716 to 6'911. Moreover, the density of the blood of women, taken in general, and without taking the buffy condition into account, is less than that of males as 6 142 to 6'575. The coagulation of the blood, also considered without reference to the production of buffiness, likewise takes place more readily in women than in men, requiring for the former a mean time 17 m. 34 s.; for the latter 22 m. 44 s."--Vol. 106. p. 116.

Comparative experiments showed that, while the mean density of buffy blood is more than a degree of the areometer less than that of the unbuffy blood, the density of the serum of the same bloods differed only of a degree; so that it may be affirmed that, "the influence of the density of the serum in the production of the buffy coat is very feeble, the principal modification in the characters of the blood depending upon its coagulation being chiefly due to the different density of the coagulable components of the blood, or to the quantity of fibrine held in the fluid state during the interval which precedes coagulation."

Some important practical results may also be deduced from these experiments upon the density of the blood. Thus: successive abstractions of blood exert an extraordinary influence in diminishing its density. From two tables which are given, we deduce that successive depletion will reduce the density of the blood more than one half; viz. from 7°.5 to 3°.5, while that of the serum is reduced only from 4° to 2°.5; whence the corollary, that "bleeding may be considered as exerting a far more evacuant effect upon the coagulable mass held in a fluid state in blood just drawn, i. e. the fibrine, than upon the materials held dissolved in the serum even after the coagulation, i. e. the albumen." A phenomenon of familiar observation, viz. that the blood at the commencement of inflammatory diseases may present little or no buff, but that in future bleedings this may become highly developed-is explained by the diminution of the density of the fluid by successive venesections. The effect may not only be observed in successive bleedings, but at different periods of the same bleeding, by examining the respective density of portions of the fluid at the beginning and end of a bleeding. Taking the mean of 40 experiments, the first portion possessed a density of 6.127 and the last of 5.96.

Another series of experiments clearly proved that the blood is rendered more dense by inducing an artificial stagnation or engorgement by means of the fillet for some time previously to opening the vein." Venous blood then, when it is prevented by any obstacle from circulating freely in its

1847] Circumstances modifying Buffiness of the Blood. 307

veins, becomes more dense, or loses a certain portion of its watery principle. Does not this fact constitute a principle pivot of the doctrine which explains oedemas, cellular dropsies, and other infiltrations, by considering them as exudations induced by obstructed circulation ?"

The density of the blood varies as regards sex and age. It is greater in the blood of men than in that of women, a mean of 90 examinations of each giving 6.437 to 6.170. In adults the density is generally greater than in children. In Summer, also, it is more dense than in Spring and Winter, owing to the more abundant transpiration which then takes place. The author has also many times observed a sudden and unusual increase in the density of the blood of certain patients who have been subjected to profuse sweatings or abundant evacuations,

(2). Temperature.-The coagulation of the blood being one of the first of the metamorphoses prior to decomposition which the blood undergoes, heat tends to accelerate and cold to postpone it.

"This fact, together with the no less important one of the lesser density of the blood during spring-time, explains to a certain extent the frequency and abundance with which blood becomes buffed at that season; for, without considering the severity of the visceral phlegmasia which prevail in the Spring as compared with the Summer, the slow coagulation of the blood favoured by the colder temperature and by its own lesser density, may, at the very least, cause an exaggeration in the appearance of the buffiness, which merits the attention of the physician, so that he may be enabled to assign their just value to the symptomatic phenomena furnished by the blood in disease."-Vol. 106, p. 137.

(3). Contact of the Atmospheric Air.-A number of ingenious experiments are related in proof, that the contact of the atmosphere favours the coagulation of the blood, just as whatever diminishes or prevents such contact retards this phenomenon. Dr. P. objects to the experiments and conclusions of Magendie, Magnus, and others, upon the influence of various gases in inducing coagulation, inasmuch as the mode of conducting the former do not allow of faith being attached to the latter. He describes at some length the precautions he himself took to secure more exact results, and concludes that nitrogen and oxygen, separately examined, do not seem to promote the coagulation of the blood more than does the air itself; indeed, if there is any slight difference, they seem to retard it: and that carbonic acid gas evidently retards the coagulation, so as to induce the formation of the buffy coat more easily than in the normal state. The oxygen, as well as the azote and atmospheric air, after having reacted on the blood which coagulated under their influence, always presented themselves loaded with carbonic acid gas, proceeding doubtless from the blood in which it had been held dissolved.

"The blood, therefore, coagulates more readily when in contact with the air and its gases than when deprived of their influence, because it yields to them more readily its carbonic acid gas: and it coagulates more tardily in carbonic acid gas, because, besides not being able to emit that which it contains, it dissolves another portion of this gas, which it cannot be doubted has the effect of still longer maintaining it in the fluid state."

(4). Nature of the Recipient.-Comparative experiments have shown that coagulation takes place more readily in glass vessels than in tin, and

much later in leaden ones. The size of the vessels, and the contact of other solid bodies, likewise exert great influence.

(5). Agitation. This, if carried to any extent, as by stirring the blood with a bundle of rods, will prevent its coagulation by depriving it of all its fibrine: but if the blood be stirred or shaken for a few minutes, and then left at rest, coagulation is only hastened. The different capacity of the vessel, or rather the different amount of the mass of the blood collected together, has, as well as the different mode it flows from the arm, great influence in determining the buffy appearance. A series of experiments showed that a small portion of blood was always longer in coagulating and more often buffy, while a large quantity coagulated quickly without buff; and this circumstance is explained by the amount of agitation kept up during the longer time the larger portion takes to flow.

"So that the mere circumstance of collecting much blood in one recipient, for the reason stated, is the cause of its coagulating more quickly, and hence hindering the appearance of buffiness which a small portion would have afforded. A quantity of blood drawn at a time may likewise mask in another manner the natural aspect of the blood. For the last portion drawn possessing a very different coagulability to the first, and coagulating generally much quicker, covers with a stratum possessed of little or no buffiness the lower strata, which of themselves would furnish much more buff, and this imparts to the blood a mendacious appearance. These facts putting us on our guard respecting the absence or slight quantity of buff in blood received during a copious venesection into only one vessel, show us the necessity of always receiving a small portion separately when we are desirous of drawing any indication from its appearance with confidence." -Vol. 106, p. 160.

3." Of the Causes of the Coagulation of the Blood, and of its slow or rapid Coagulation in Diseases.

"From the preceding observations we may infer that the appearance or nonappearance of buffiness of the blood is a phenomenon chiefly dependent upon and expressed by the time employed in its coagulation, notwithstanding that some other circumstances may secondarily induce certain modifications; and the object is now to inquire what is the cause of the ready or tardy coagulation of the blood when removed from the living economy, as this alone gives value to the presence or absence of the buff, when we wish to draw conclusions from the aspect of the blood in disease."

All circumstances which tend to increase physiologically or morbidly the activity of the animal functions lead to a slower coagulation of the fibrine of blood removed from the body; and all the circumstances producing a diminution of vital power lead to its more ready consolidation. This is seen in the more ready coagulation of the blood of women than that of men-the diminution of the power of the fibrine to hold itself in the fluid state in proportion to the amount of blood taken, and to the lateness of the period of the bleeding during which it is examined-the prompt coagulation which takes place on the induction of syncope and of general or partial obstruction of the circulation-and the greater readiness with which it may be induced in the blood of small and weak animals than in large and strong ones. Whence we may conclude

"1. That the consolidation of blood drawn from a living animal is a phenome