558 SPECIAL HISTOLOGY. 



Mammals, and perfectly identical in their structure with the larger tra- 

 beculce. Other fibres which occur in the pulp are plainly the termina- 

 tions of the vascular sheaths. They are very numerous, and usually 

 have the appearance of delicate, indistinct, fibrous membranes, without 

 any elastic element, which appear to connect the capillaries, and are, 

 perhaps, continuous with the finest trabeculce. 



The cells of the pulp, or parenchyma-cells of the spleen, round cells 

 of 0-003-0-005 of a line, with single nuclei, are for the most part so 

 similar to those in the Malpighian corpuscles, that it is unnecessary to 

 enter upon a more minute description of them ; intermingled with them, 

 and, indeed, in larger quantities than in the Malpighian corpuscles, we 

 find free nuclei. Besides these, a few other elements may be met with : 



1, pale round bodies, with a homogeneous aspect, somewhat larger 

 than the corpuscles of the blood, which appear either as free nuclei, or 

 as homogeneous nuclei, closely surrounded by a delicate investment ; 



2, larger cells, up to 0-01 of a line in diameter both of the completely 

 pale kind, with one or two nuclei, and also what I have called colorless 

 granule-cells that is, cells with more or fewer colorless, dark fat-gra- 

 nules. Each of these elements exists in the splenic corpuscles also, but 

 never to so great an amount. The quantity of the different kinds of 

 parenchyma cells and of free nuclei in the pulp, is so considerable, 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 trabeculce 

 and vessels of every description, and surround the Malpighian corpus- 

 cles. The clearest conception of the arrangement is obtained, if we 

 consider that every segment of the red substance included within the 

 larger trabeculce has the same composition, on the small scale, as the 

 whole spleen has on the large. In fact, the microscopic trabeculce, the 

 terminations of the vascular sheaths and the finest vessels, present the 

 same relations as the large trabeculce 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 everywhere in direct contact 

 with the sheaths of the vessels, the trabeculce, and the sheaths of the 

 Malpighian corpuscles. 



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

 color at different times ; or rather the blood-corpuscles which it contains 

 and which, without the participation of any other element, give rise to 

 its color, present different conditions. In some animals, for instance, 

 its color is sometimes paler, more grayish-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 demonstrated that the red 



