The pathological evidence that the red cor puscles are not the elaborators of the fibrin, appears to the writer to be quite conclusive. Whilst the quantity of fibrin is so remarkably increased in inflammation, the number of red corpuscles undergoes no decided change. Again, the augmentation of the fibrin is not in compatible with a chlorotic state of the blood ; the peculiar characteristic of which is a great diminution in the proportion of red corpuscles. By such alterations, the normal proportion be tween the fibrin and the red corpuscles, which may be stated as A : B, may be so inuch altered, as to become, in inflammation, 3a : B, in chlo rosis A : A B. Again, in fever, the characteristic alteration in the condition of the blood appears to be an increase in the amount of red cor puscles, with a diniinution in the quantity of fibrin ; yet if a local inflammation should establish itself during the course of a fever, the proportion of fibrin will rise ; and this without any change in the amount of corpuscles. Lastly, the effect of loss of blood has been shown by A ndral's investigations to be a marked diminution in the number of red corpuscles, with no decided reduction in the quantity of fibrin, even when this is much above its normal standard ; and in this-condition of the blood it has been observed by Remak that the colourless corpuscles are very numerous.
Formation tissue.—With the elaboration of the alimentary materials into fibrin, the pre paratory processes of nutrition may be regarded as terminating ; since the next step is the trans formation of this substance into organised tissue. Upon the mode in which this is effected, much light has been thrown by recent enquiries ; but several points still remain obscure. We shall endeavour, in the following account, to dis tinguish what has been satisfactorily ascertained from what is merely hypothetical.
That the particles of perfectly-elaborated fibrin are capable, in solidifying-, o [spontaneously assuming a definite arrangement, cannot now be questioned. In the ordinary crassamentum of healthy blood, this arrangement can be seen, by examining thin slices under the microscope ; especially after the clot has been hardened by boiling. A number of fibres, more or less dis tinct, may be seen to cross one another ; form ing by their interlacement a tolerably regular network, in the meshes of which the red cor puscles are entangled. This fact was known to Ilaller ; but it has been generally overlooked by subsequent physiologists, until attention %vas drawn to it by the enquiries of Messrs. Addison, Gulliver, and others. It is in the buffy coat, however, that the fibrous arrangement is best seen ; on account, as it would appear, of the stronger attraction which the particles of fibrin have for one another, when its vitality has been raised by the increased elaboration to which it has been subjected. That there are varieties of plasticity in the substance, which, on account of its power of spontaneously coagulating, we must still call fibrin, appears from this fact among others,—that, in tuberculous subjects, the quantity of fibrin in the blood is higher than usual (Andral and Gavarret), although its plasticity is certainly below par. It is easy to
understand, that its plasticity may be increased as that it may be dinainished ; and this either in the general mass of the blood, or in a local de r;sit. In fact, the adhesions which are formed the consolidation of coagulable lymph,--or in other words, of liquor sanguinis, whose plas ticity has been heightened by the vital actions of the white corpuscles in the capillaries of the part on which it has been effused,—often acquire very considerable firmness, before any vessels have penetrated them ; and this firmness must depend upon that mutual attraction of the panicles for one another, which in °plastic de posits is altogether wanting, and which in eaco-plastic deposits is deficient. A very inte resting example of a structure entirely composed of matted fibres, and evidently originating in the simple consolidation of fibrin, has lately been discovered by the writer. This is found in the membrane adherent to the interior of the egg-shell (membrana puta.minis); and also in that which forms the basis of the egg-shell itself. Between the two, there is no essential difference; as may be seen by examining " an egg without shell," as it is commonly termed, (or rather one in which the shell-membrane has been uncon solidated by the deposition of calcareous matter); or by treating the egg-shell with dilute acid, so as to remove the particles of carbonate of lime, which are deposited in the interstices of the net work. The place of the shell is then found to be occupied by a membrane of considerable firmness, closely resembling that which sur rounds the albumen of the egg, but thicker and more spongy. After maceration for a few days, either of these membranes may be separated into a number of laminm, each of which (if suf ficiently thin) will show the beautiful arrange ment of reticulated fibres, which is delineated in the accompanying figure (fig. 405). It is impossible to refuse to such a structure the desig nation of an organised tissue, although itcontains no vessels, and must be formed by the simple consolidation of fibrin,poured out from the lining membrane of the oviduct of the bird. It is probably in the same manner, that the chorion of the mammiferous animal originates; since this is a new envelope, formed around the ovum, during its passage along the Fallopian tube. In the latter, for an ulterior purpose, vessels are afterwards developed, by extension from the contained ovum ; and by the nutrition they supply, its size is increased, and changes take place in its texture. But in the egg-membrane of the bird, there is no need of vessels ; because no subsequent change in its texture is required, and its duration is sufficient for the purpose it has to answer.