148 SPECIAL HISTOLOGY. 



that, together with a small amount of a reddish yellow 

 fluid which unites them, they constitute probably one-half of 

 the bulk of the spleen. They are not collected in large 

 masses, but in small irregular aggregations of different sizes, 

 which occupy the interspaces between all the trabecule and 

 vessels of every description, and surround the Malpighian cor- 

 puscles. The clearest conception of the arrangement is ob- 

 tained, if we consider that every segment of the red substance 

 included within the larger trabecule has the same composition, 

 on the small scale, as the whole spleen has on the large. In 

 fact, the microscopic trabecules, the terminations of the vascular 

 sheaths and the finest vessels, present the same relations as 

 the large trabecules and vessels, while the small masses of 

 parenchyma cells correspond with the apparently homogeneous 

 masses of pulp, visible to the naked eye. There are no special 

 investments around the parenchyma-cells, but they lie every- 

 where in direct contact with the sheaths of the vessels, the 

 trabecule, and the sheaths of the Malpighian corpuscles. 



The red pulp of the spleen of Man and of Animals has a 

 different colour at different times; or rather the blood-corpuscles 

 which it contains and which, without the participation of any 

 other element, give rise to its colour, present different condi- 

 tions. In some animals, for instance, its colour is sometimes 

 paler, more greyish-red, sometimes brown, or even blackish-red. 

 In the latter case, a quantity of changed blood-corpuscles will 

 be met with (to which we shall return subsequently); in the 

 former, on the other hand, it may be microscopically demon- 

 strated that the red colour proceeds from unchanged blood-cor- 

 puscles, which may also be readily expressed from the sub- 

 stance of the spleen and, on the addition of water, in a 

 short time lose all their colouring matter. In other animals 

 the spleen, although it always has about the same, usually 

 dark colour, yet contains in addition, sometimes only un- 

 changed blood-corpuscles, sometimes multitudes of them in 

 every stage of metamorphosis. These are very striking, and 

 in all animals consist essentially in this — that, 1. the blood- 

 corpuscles, becoming smaller and darker and, in the lower 

 Vertebrata, losing their elliptical form and taking a circular 

 shape, agglomerate together into rounded masses, which either 

 persist in this condition, or, combined with a certain amount 



