In the case of haemorrhage by diapedesis and in most haemorrhagic infiltrations, the blood, being in the serous spaces and in communication with the lymphatics, is readily carried oft'. Before it is finally disposed of in' this way, however, it may have undergone changes, especially in the red corpuscles, such as result in a greater or lesser degree of pigmentation. These changes are, however, similar to those about to be mentioned as occurring in larger haemorrhages.

In larger haemorrhages the blood forms a mass and coagulates, while at the periphery there is a certain amount of infiltration into the surrounding tissue. An early phenomenon is the solution of the haemoglobin of the red corpuscles. A red solution is thus formed which may stain the tissues for some distance around. The peculiar bright red colour which one sees in the neighbourhood of a haemorrhage in the brain, or the various colours seen in the skin after an effusion of blood into it, are due to staining of the tissues with the dissolved colouring matter of the blood, but neither of these is permanent. As the pigment is dissolved it will pass off with the fluid into the lymphatics, and the staining, while it may be somewhat extensive, will be evanescent.

A more durable Pig-mentation may result in two different ways. In the first place, the colouring matter after being dissolved out of the corpuscles is often, after a time, deposited in the solid form, appearing as crystals of haema-toidin (see Fig. 34), or as granules. This solid pigment is somewhat permanent. In the second place, the red blood-corpuscles may be taken into the substance of other cells, and so disposed of. (See Pathological Pigmentation).

If the blood is considerable in amount it comes to be treated as a piece of dead animal matter in the midst of the living tissues. Inflammation occurs around it, and this leads to what is called Organization of the clot. In this case the process is very similar to that already referred to in the organization of the thrombus (which see), and the result is usually the formation of a cicatrix. Sometimes a process in some respects similar to the formation of cavernous tissue in place of the thrombus occurs, but instead of the meshes being filled with blood they are filled with serous fluid. Thus in the case of a haemorrhage in the substance of the brain the new-formed connective tissue which replaces the effused blood is unable from the brittle nature of the brain tissue, and from the fact that it is contained in a closed rigid cavity, to form a cicatrix by its contraction. Instead of that, by its contraction it leaves spaces which are filled with serous fluid, and so we have the apoplectic cyst.

An old clot which is not in a position to be readily disposed of in any of the ways described may dry in and finally become impregnated with lime salts. It need hardly be said that when exposed to septic influences a clot is liable - perhaps very liable - to undergo decomposition.

Fig. 34. - Crystals of hsematoidin from an old haemorrhage in the brain. Their colour is reddish brown, x 350.

Literature

Haemorrhaye by diaperiesis - Stricker, Sitzungsber. d. Wien. Akad., 1865-66-67; Cohnheim, Virch. Arch., xli. and xlv., and Allg. Path., i., 368; Arnold, Virch. Arch., lviii., 203, 231. Haemophilia - Blagden, Med. Chir. trans., viii., 224, 1820; Wickham Legg, Treatise on H., 1872; Grandidier, Die Hamo-philie, 1877; Recklinghausen, Allg. Path., p. 91; Virchow, Deutsch. Klinik, 1856. Purpura - Russell, Brit. Med. Jour., Sept., 1883; Watson Cheyne, Path, trans., xxxv., 1884. Arrest of haemorrhage - Stilling, Proc. bei d. Heilung der Blutgefiisse, 1834; Paget, Lectures on Surg. Path., 3rd. ed., 1870. Hematoma - Virchow, Geschwulste, i., 144.