SECT. 



1 68.] PARENCHYMA OF THE SPLEEN. 36$ 



which contain dark, fat-like grannies, without colour, and these I 

 have named the ' colourless granular cells ' of the spleen. These 

 two last elements are found also, but in smaller numbers, in the 

 Malpighian corpuscles. The various cells of the parenchyma are 

 united by a small quantity of reddish-yellow fluid, and their 

 quantity is so considerable as to form, probably, one-half of the 

 entire red substance of the spleen. They are not aggregated into 

 large collections, but form small irregular heaps of different sizes, 

 occupying the interspaces between the trabeculse, the vessels, and 

 the Malpighian corpuscles. The arrangement may be most cor- 

 rectly understood, if we consider each segment of the red substance 

 enclosed between the larger trabeculse as representing a spleen in 

 miniature. In fact, the microscopical trabeculse, the terminations 

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

 same arrangement as the corresponding larger structures visible to 

 the naked eye ; and the microscopical collections of pulp- cells 

 may, in the same manner, be said to correspond with those larger 

 segments of the parenchyma, which, to the unaided sight, appear 

 homogeneous. Nowhere is there any special investment found to 

 surround the parenchyma-cells, but they lie directly in contact 

 with the sheaths of the vessels, the trabeculse, and the envelopes 

 of the Malpighian corpuscles. 



The red pulp of man and of animals presents, at different times, 

 a different colour, or, rather, a different behaviour of the contained 

 blood- corpuscles, for on this condition especially depend the va- 

 riations in colour. In one kind of animal it will present at one 

 time a paler and greyish-red colour, while at another time it 

 will be found brown or blackish-red. In the latter case, there are 

 found a number of altered blood-corpuscles, of which we shall 

 further have to speak ; in the former case, on the other hand, it 

 can be readily demonstrated, by microscopical examination, that 

 the red colour is derived from unaltered blood-discs, which can 

 also be readily pressed out of the tissue of the spleen, and, on the 

 addition of water, soon give off all their colouring matter. In 

 other animals, however, the spleen has always a pretty steady 

 colour, which is generally dark ; but in these, also, the blood-cor- 

 puscles are sometimes found unaltered, at other times, many of 

 them arc seen to be undergoing metamorphoses of various kinds. 

 Now these metamorphoses arc very striking and peculiar, and, in 

 all animals, essentially depend upon the following changes: 1. The 

 blood-globules, becoming smaller and darker, collect together in 

 roundish heaps, the elliptical blood-corpuscles of the lower verte- 



