COMPARATIVE HISTOLOGY AND PHYSIOLOGY OF THE SPLEEN. 283 



plate-like. The cellular elements of the pulp in the adult spleen are mainly lymphoid 

 cells, small and uninucleated, like those of the outer zone of the follicles ; but a few are 

 larger and resemble the cells of the germinal centre. Protoplasmic corpuscles are 

 comparatively few in number. Several spleens of adult cats were examined, and in only 

 one of them giant cells were found, and in it there were not more than four in a section. 

 Their nuclei were nearly always clustered in a ball near the middle of the cell, round 

 which was found a comparatively narrow band of granular protoplasm that had a 

 distinctly yellow hue when the section was stained with hasmatoxylin only. 



The cellular elements in the young and functionally active spleen show marked 

 differences. The spleens of five kittens, of different ages, were examined — one six 

 weeks old, one ten days, one about a week, one three days old, and one at birth, and 

 in all of them the conspicuous feature is the presence of giant cells. These are most 

 numerous in the seven days' spleen, numbering on a rough estimate about ten thousand 

 in a section, and, as one would expect, the whole spleen was much enlarged. In the ten 

 days old spleen they number about five hundred in a section, in the six weeks' spleen 

 about fifty, in the three days' spleen about forty, and in the spleen at birth about 

 twenty in a section. 



In the Kitten at birth the giant cells appear to be especially situated in the pulp 

 that surrounds the smaller veins. Their average size is 20 /x in length by 30 /a in 

 breadth. The cell protoplasm has a conspicuous hyaline rim, which has a more pro- 

 nounced yellow colour than the rest. In most of the cells the nuclei are grouped 

 centrally, but in some as many as eight nuclei are scattered throughout the substance 

 of the cell, and occasionally a knob-like portion of a nucleus that is attached or apposed 

 to the central heap projects beyond the general outline of the cell. A few of the 

 giant cells show vacuoles. Around the giant cell are frequently grouped cells having 

 the characters of erythroblasts. There are with them similar but smaller cells with 

 more deeply stained nuclei. 



In the three days old Kitten the cellular elements are practically the same in 

 character as those of the newly-born kitten. The nuclei of the giant cells are nearly 

 always collected in a spherical heap near the centre of the cell. A remarkable feature, 

 as in the spleen last described, is the presence of large oblong free masses of pig- 

 ment both in the pulp and in the veins. Although the colour of the red blood- 

 corpuscles is slightly the darker, there is a strong presumption that the invariable 

 yellow colour of the giant cells and of the erythroblasts is due to the presence of 

 haemoglobin. 



In the spleen of the Kitten about a tveek old the nuclei of the giant cells are 

 usually grouped together near the middle of the cell, and the groups are frequently 

 separated from the protoplasm by a perinuclear space. When the individual nuclei are not 

 close together, they are often seen to be connected by threads of chromatin. Some of the 

 groups of nuclei are practically unstained with hematoxylin, while those of neighbouring 

 cells may be deeply stained. The giant cells are much more irregular in outline than 



