If a clot of blood be gently kneaded and pressed under a stream of water, it gradually becomes and finally loses its red colour entirely, the colouring matter being washed away; what remains in the hand is a mass of whitish and very elastic filaments composed of fibrine. Or otherwise, if, instead of being left at rest, a quantity of freshly drawn blood be quickly stirred with a bundle of rods, a stringy mass of fibrine will be found adhering to these after a time, and the blood thus treated will not coagulate. This experiment shows that it is to the fibrine that the blood owes its pro perty of coagulating.
The filaments of fibrine studied under the microscope are found to be formed by the aggregation of a multitude of white globules, bearing the greatest resemblance to the central nuclei of the proper globules of the blood. It was, therefore, natural to suppose that the formation of the coagulum depended on the spontaneous decomposition of these globules and the aggregation of their internal corpuscles. And such, indeed, is the theory which Messrs. Prevost and Dumas have given, and which has been adopted by the greater number of the physiologists of the present day. 44 The at traction," say they, " which keeps the red matter fixed around the white globules having ceased along with the motion of the fluid, these globules are left at liberty to obey the force which tends to make them combine and form a net-work, in the meshes or amid the plates of which the colouring matter is included along with a great quantity of particles which have escaped this spontaneous decomposition." It would appear, however, that this is not an exact explanation of the phenomenon, for Professor Muller, of Berlin, has succeeded in demonstrating that the coagulation of the blood is altogether independent of the globules, and that the fibrine which determines the pheno menon exists dissolved in the serum. By filter ing with great care the blood of frogs, diluted with sugar-water, he separated the globules completely from the serum before coagulation took place : the fluid part of the blood alone passed the filter, the solid particles remained upon it ; nevertheless, a coagulum formed within the fluid after the lapse of a few mi nutes; this, of course, was colourless instead of red, as it is when the red globules are en tangled in the mass. This curious and in teresting experiment does not succeed so well when human blood is employed, inasmuch as the globules, being much smaller than those of the blood of the frog, pass along with the serum through almost any filter that can be used. Still Professor Muller has succeeded in proving the existence of fibrine in the serum by means of the following procedure. If to a little blood contained in a watch-glass a few drops of a highly concentrated solution of sub carbonate of potash be added, the coagulation of the fluid is so much retarded, that the glo bules have time to sink to the bottom before it occurs. When coagulation takes place at
length, the clot extends as usual through the whole mass, but it is colourless on its upper part, and only red in the part into which the globules have subsided. Professor Muller believes that the fibrine exists in a state of solution in the serum, an opinion which to us appears hardly reconcilable with the known che mical properties of this substance ; we are more inclined to suppose that, like the proper glo bules, it is merely suspended in the mass of the blood in a state of extreme subdivision, and possessed of transparency too perfect to admit of its being distinguished amidst the sur rounding fluid.
There are circumstances under which the blood only coagulates with difficulty, or in which it even loses this property entirely. In cases of poisoning with hydrocyanic acid, for instance, the blood remains fluid and thick after death ; the same thing also occurs after death from fever of a typhoid type, from lightning, &c.
Another phenomenon presented by the blood which is of very common occurrence, and depends on the manner in which it coagu lates, consists in the formation of what is called an inflammatory crust or bey coat : the coagulum, instead of being uniformly red, then appears covered with a greyish or yel lowish viscid and very tough pellicle of various degrees of thickness. The pheno menon in question is principally observed in individuals labouring under acute inflammatory affections of the serous or synovial membranes, of the substance of the lungs, &c. but also occurs among persons in good health, although plethoric. The experiments of M. Ratier go to prove that various circumstances, altogether independent of the physiological state of the individual, may also exert great influence on the formation of the buffy coat : thus, cceteris paribus, it is more readily produced if the blood withdrawn be received in a deep and narrow vessel, and. if the opening in the vein be large, and the jet be free. The cause of the buffy coat has been very satisfactorily ex plained; it depends on the more rapid subsi dence than usual of the red globules, in con sequence of which the more superficial parts of the coagulum contain none. From the ex periments of Professor Muller it would also appear that this subsidence of the globules takes place more quickly if a thick solution of gum be added to the blood, so as to increase its density, whilst, when it is deprived of its fibrine by stirring with rods, these bodies remain for a very long time suspended. Nov it follows, from the investigations of Sir C. Scudamore, that buffy blood contains a larger proportion of fibrine than usual, a state to which the more rapid deposition of the glo bules, and the formation of the inflammatory crust, which is its consequence, may be at tributed.