gas exists in both the venous and the arterial blood of man, but that as much as two cubic inches could be extracted from every ounce of blood. Sir Everard did not use this statement as one particularly bearing on coagulation, but as supporting an hypothesis that as, in the coagulation of dead blood, channels are made in it by the escape of carbonic acid, so in the living body effused blood may be made vascular by the blood-vessels transmitting blood into it, by channels similarly produced.

Mr. Bauer seems to have been the first observer who stated that blood in coagulating exhales carbonic acid. Contrary to the views of Scudamore regarding carbonic acid, Dr. John Davy held that the agitation of carbonic acid gas with blood does not retard coagulation; that newly drawn blood really absorbs carbonic acid; and that water charged with this gas and added to blood does not affect the coagulating process.

Without endeavouring to define its nature, Spallanzani conceived that there was in blood an elastic invisible gas. In this view he was supported by his English translator, Dr. Hall, who urged this point on the notice of physiological inquirers, as one deserving special notice, and as promising to explain many of the phenomena connected with the blood and circulation.

In speaking of the various chemical hypotheses which have been raised regarding coagulation, it would be an error to omit that which is held by Schmidt and Schulz, and in some degree supported by the writings of Mulder; viz., that fibrin, per se, does not exist in the circulating living blood at all. Schmidt's arguments are intended to prove "that, as blood escapes from the circulation into a cup or other vessel, an acid albuminate of soda, which previously existed in a state

of solution in the Blood, beermes disintegrated into its omrigerent parts in such a manner that a less acid, meatral, er basic albuminate of soda remains dissolved;

be the ether atom ef albumen separates under the form of protein, which we call fibrin." The fibrin thus hered and separated, afterwards contracts into the smallest possible volume, just as freshly precipitated slica, alumina, and phosphate of lime contract when isolated. Respecting this peculiar hypothesis, Lehmann, to whom I am indebted for its history, observes, that if we watch the separation of fibrin into filaments during coagulation, it will be seen that "the analogy with hydrated alumina affords no special support to this hypothesis, which, at first sight, seems sufficiently plausible.”

EFFECTS OF ELECTRICITY AND GALVANISM.

Gerhard and Hufeland, according to F. Simon, have shown by experiment that an electric current, continuously passed through blood, tends to keep that fluid in an uncoagulable state. Scudamore tried the effects of both electricity and galvanism on drawn blood. The results of his experiments, with reference to electricity, ditor from those of Hufeland and Gerhard. He found that blood exposed to the electric current gained in temperature two degrees on the introduction of the current, but coagulated as soon as did other blood removed at the same time from the same person and allowed to concrete naturally; and again, that the blood tivated by electricity coagulated more firmly. In experimenting with the galvanic current, he found also that the temperature of the blood was raised. one case there was a copious evolution of gas at the negative pole, and in all cases the current gave rise to a peculiar process of coagulation and decomposition.

In

PHYSICAL INTERCHANGES IN THE CONSTITUENTS OF THE BLOOD.

Of late years, an hypothesis has been gaining ground, that the fluidity of the blood is sustained during life by the constant abstraction of fibrin from the circulation for the purposes of nutrition. This idea was hinted at indeed very broadly by Dr. Bostock, in the passage I have already quoted from his work. "As fibrin," he says, "is gradually added to the blood, particle by particle, while that fluid is in a state of agitation in the body, it (the fibrin) has no opportunity of concreting." The idea present in Dr. Bostock's mind evidently was that fibrin passes from the heart to the extremities of the circulation without any change by the way; and that, having arrived at its destination, it enters into the construction of such solids as receive it as a part of their structure. '

By another and more extended view, it has been conceived that the liquor sanguinis, being constantly pervaded by the red blood corpuscles, is elaborated by them, and that the coagulable part is thus taken up as quickly as it is formed. This view is maintained by Mr. Wharton Jones, who does not, however, here undertake to answer the question, whether the process of coagulation be a vital or a physical one? but prefers to explain, as above, why the blood circulating in the living body does not coagulate. By an extension of this view, Mr. Jones argues further, that the elaboration supposed to be performed by the red corpuscles is probably the conversion of one protein compound into another, albumen into fibrin, a less into a more highly organised proximate principle.

Mr. Gulliver points out that this hypothesis is an old

one revived; that it was virtually advanced by Quesnay in 1750, and by Bordenave in 1787. He objects to it, as well as to the hypothesis that fibrin is elaborated by the white corpuscles, on the ground "that fibrin and its fibrils may be produced merely by mixing together certain varieties of serum, in which, before mixing, no fibrinous particles can be discovered by the microscope." Mr. Dowler shewed that in the fluid produced by a blister there exists a fibrous part, which can be extracted by squeezing the fluid strongly through a fine linen cloth. The fibrous part is left on the cloth, and resembles the fibrin of blood. This observation, though important, is, however, less pointed, since it may be urged that coagulable lymph is effused, under the blister, with the serum.

An hypothesis of the physical kind which is advocated by some authorities is, that the period and the intensity of coagulation depend on the quantity of fibrin, in relation to the blood corpuscles and water. When the corpuscles are few in proportion to the quantity of fibrin, the molecules of fibrin become more densely compressed together, and thus render the formation of the clot more marked, and its structure more firm. (Lehmann, vol. ii, p. 199.)

A further hypothesis, which is in part physical and in part chemical, is advanced by Dr. Carpenter: viz., that coagulation consists in the passage of blood from the soluble to the insoluble state, in which transition it is not formed into an amorphous coagulum, but into a network of fibres more or less definitely marked out. In a former page we saw that Dr. Carpenter considered coagulation to be a vital process. However, we now find him defining the process on simple principles.

Prevost and Dumas, in speaking of coagulation,

thought that the red corpuscles were essential to that process. They contended that "the attraction which keeps the red matter fixed around the white particles having ceased when blood is drawn, together with the motion of the fluid, these parts remain at liberty to obey the force which tends to make them combine and form a net-work, in the meshes or amid the plaits of which the colouring matter is included, with a quantity of particles which have escaped this spontaneous decomposition." This speculation, as M. Edwards indicates, was entirely disproved by Müller, who shewed that when the blood corpuscles were filtered off from newly drawn blood, prior to coagulation, the fibrin now left with the serum alone spontaneously solidifies. It was further disproved by Dr. Babington, to whom we owe the term liquor sanguinis, as distinguishing the fluid in which the red corpuscles float during life. This liquor sanguinis he believes to be no mere mixture of fibrin and serum during life, but a homogeneous mass, which, after the vital force is removed, separates into two distinct parts; one part spontaneously coagulable, the other fluid at ordinary temperaturesfibrin and serum. Dr. Babington skimmed off the liquor sanguinis from blood, and observed the coagulation as a process independent of the corpuscles.

SPECIFIC GRAVITY.

The specific gravity of the blood, or of its parts, has been thought to bear some relation to the rapidity and cause of coagulation. On this point it has been shown. that viscid solutions, such as albumen, or thick solution of gum, introduced into newly drawn blood, tend materially to retard coagulation; and that by this means a buffy coat may be produced from healthy blood. Hence it has