COMPARATIVE HISTOLOGY AND PHYSIOLOGY OF THE SPLEEN. 301 



With regard to Dr Mum's estimate of the number of nucleated red cells in the spleen, 

 obtained by examining a scraping of its surface, it must be borne in mind that such 

 a preparation contains elements derived from other sources than the pulp (those from 

 the follicles being in great numbers), and cannot, therefore, be fairly compared with 

 a fresh preparation of bone-marrow, that corresponds, practically, solely with the 

 pulp. 



In the Spleen of the Dog from Experiment II. there are large numbers of giant 

 cells, — on a rough computation about 1000 in each section through its thickest part. 

 They present the usual characters, but their outline shows an unusually large number of 

 mouth-like openings. Their nuclei exhibit much budding ; perhaps the most frequent 

 arrangement is a rosette of pyriform buds. A few cells show karyokinetic figures. 

 There were no giant cells observed within the follicles. (Plate III. fig. 23.) There are 

 enormous numbers of erythroblasts and nucleated red cells present, many of the former 

 being clustered around the giant cells. There were very many more nucleated red cells 

 and erythroblasts in the blood of the splenic vein than in that of the artery. The 

 protoplasm, both of the giant cells and of the erythroblasts, has a marked yellow colour. 

 A few eosinophilous cells are present in the pulp. 



In the Spleen of the Dog from Experiments I. and III. there are equally large 

 numbers of giant cells — about 1000 in a section. Their outline has fewer mouth-like 

 openings (than in Expt. II.), but their nuclei show similar budding. The typical 

 arrangement is a rosette of pear-shaped nuclei, their apices, which point inwards, being 

 frequently connected together ; occasionally a single cell has two such rosettes, one 

 arranged around each end of a somewhat thick stem. Rarely a giant cell may be seen 

 within a follicle. Almost all the cells in the follicles are leucoblasts, and this fact, 

 together with the presence of numerous giant cells in the pulp, remind one of the appear- 

 ances in the spleen of the young Mammal. There are very large numbers of erythro- 

 blasts and nucleated red cells, but not so many as in the previous spleen ; and there 

 is a comparatively small number of these cells in the veins. Pigment-holding cells are 

 present in large numbers, and also globular masses of free, or apparently free, pigment. 

 Eosinophilous cells were not found. A considerable amount of a coarsely granular sub- 

 stance was seen in the veins, some of it collected into round clumps, and some of it in 

 the form of discrete coarse granules ; as it so nearly constantly occurs in the veins in 

 association with the giant cells in the pulp, it is suggestive that it may possibly result 

 from the breaking down of the inner coarsely granular portion of the protoplasm of the 

 giant cells. 



In the Spleen of the Dog from Experiment IV., the most striking naked-eye 

 character of which is its pale lemon-yellow colour, there are considerable numbers of 

 giant cells, but not so many as in the other two spleens — numbering, on a rough 

 estimate, about 500 in a section. This spleen is smaller than the other two, and the 

 body-weight of the dog from which it was obtained was a third less. 



Many of the giant cells are smaller — only about half the average size of those in the 



VOL. XXXVIII. PART II. (NO. 8). 2 S 



