PIGMENTATION. 59 



forms of pigmeiittition ; on the other, in the fact that a patholo- 

 gical excess of pigment in the lungs is met -svitii under those 

 very conditions of hypergemia and haemorrhage which cause a 

 deposit of pigment in other organs. It may plausibly be 

 imagined, moreover, that the blood-pigment, in a locality where 

 the osmotic interchange of gases is so extr aordinjirily active, 

 may be converted by an imperfect process of combustion into 

 animal charcoal more speedily than elsewhere. 



§ 57. Turning our attention to pathological chromatoses, we 

 find, as was hinted in our introductory remarks, that the great 

 majority of these are due to local disturbances in the circulation. 

 They are singularly persistent; they serve, accordingly, as 

 evidence not only of existing congestions, but of former hyper- 

 Kmic states of this or that organ, or part of an organ. It is 

 hardly necessary to add that not every hyperasmia is followed 

 by a deposit of pigment ; nay, we may almost consider it a rule 

 that only those congestions, during which extravasation of blood, 

 or its permanent stagnation in the vessels occurs, are followed 

 by pigmentation. This assertion will seem less rash if we reflect 

 that apart from haemorrhages of notable amount, both acute 

 inflammation and passive congestion give rise to minute but 

 proportionately numerous extravasations from the capillaries. 

 But it relies for its ultimate justification on the evidence of 

 anatomical facts. 



All purely local pigmentations, i.e. those which are not con- 

 nected with dyscrasiae, may be shown to originate in the abso» 

 lute stagnation of variable quantities of blood ; sometimes of 

 only a few blood-corpuscles wdiich have not even succeeded in 

 completing their escape from the vessel, but have stuck in the 

 tunica adventitia; more frequently of little streaks and drops of 

 blood, or even larger collections, which lie in the parenchyma 

 outside the vessel. "We need not enter into the manifold changes 

 to which such stagnant portions of blood arc liable (organisa- 

 tion, suppuration, &c.) ; we may confine ourselves to an observa- 

 tion, which is of the utmost moment as regards the production 

 of pigment, viz. that the red discs generally lose their colouring- 

 matter, which is thus at the disposal of the neighbouring tissues 

 in a state of solution. We had the opportunity of becoming 

 acquainted with a process not unlike this during the putrefaction 

 of the blood. It follows accordingly that decolorisation is a- 



