220 MOKBID STATES OF THE BLOOD, ETC. 



the spleen, whose peculiar structure excludes the possibility of 

 extravasation, since the blood could only be extravasated out of 

 one of its natural channels into another, the pigmentation occurs 

 in the intervascular cords of the pulp — in those parts therefore 

 where the blood flows most slowly. Even under normal condi- 

 tions we may here observe the development of pigment-cells and 

 blood-corpuscle-holding cells (cf. note to § 57). In the pig- 

 mented spleen the intervascular cords are so thickly packed with 

 the black, flaky masses (fig. 70, h) that the organ presents even 

 to the naked eye a colour varying from slate-grey to black (the 

 milza nera of the malarious districts of Italy). 



From hence the pigment-flakes make their way into the 

 blood. We know that the intervascular cords are not shut 



Fig. 70. 



The melaneemic spleen. Transverse section from the middle 

 of the organ, a. The cavernous veins of the spleen; h. 

 The intervascular cords containing pigment ; c. A branch 

 of the splenic artery. 3^. 



off from the cavernous veins by an impermeable membrane 

 (fig. 70, a) ; we regard the former in the light of a filter with 

 very fine pores intercalated between the arterioles on the one 

 hand, and the venous radicles on the other, and which, in the 

 spleen, takes the part of the capillary vessels and parenchyma of 

 other organs. During this filtration the pigment-flakes are 

 torn from their place of origin and pass into the blood, where 

 their presence gives rise to the melanmiaec dyscrasia. The black 

 particles are accordingly carried wherever the blood itself pene- 

 trates. We find them in all the organs of the body, especially 

 in those which are characterised by the narrowness of their capil- 

 laries, e.c;. in the brain. All the flakes cannot pass through this 



