COMPARATIVE HISTOLOGY AND PHYSIOLOGY OF THE SPLEEN. 289 



numbers of giant cells occur ; they are most numerous in a spleen obtained during 

 hibernation (numbering about 1000 in a section) ; but they are nearly as numerous 

 (about 800 in a section) in a summer spleen, obtained in July ; while in a March 

 spleen they are less numerous (about 600 in a section) ; and at the beginning of 

 hibernation in one (October) spleen they number about 250, but in another (November) 

 spleen they number about 800 in a section. In each case the size of the spleen varies 

 directly with the number of giant cells. 



The other kinds of cells present in the pulp are lymphoid cells, erythroblasts, and a 

 few pigment-holding cells that are found principally within the hilar sheath around the 

 larger arteries. 



There are well-marked karyokinetic figures in the giant cells, in the erythroblasts, 

 and in the protoplasmic corpuscles of the follicles. The figures are most numerous, as 

 regards the giant cells, towards the end of hibernation ; in a March spleen there are about 

 twenty in a section, occasionally two are seen in one field of the microscope ; they were 

 also fairly numerous in the spleens of two hibernating animals during the autumn 

 (October and November) months. The converse obtained as regards karyokinesis in the 

 protoplasmic corpuscles of the follicles ; figures were plentiful in the summer and autumn 

 spleens, but scarce or absent in the hibernating spleens. 



The nuclei of the giant cells show much variety in arrangement ; the most frequent 

 is that of a central heap of closely apposed nuclei, sometimes as many as fifty or sixty 

 in one cell. Often there may be seen a large number of pear-shaped nuclei, not apposed 

 but isolated, yet near together, arranged in a radiating manner, the ends of the stalks of 

 the pear-shaped bodies being near the centre, and their rounded ends near the periphery 

 of the cell. Occasionally all the nuclei are isolated round bodies scattered nearly 

 regularly throughout the substance of the cell. Sometimes an oval nucleus is seen to be 

 connected with the central heap by a long thread of chromatin, being apparently on the 

 point of separation. In some of the giant cells there is a distinct perinuclear space, 

 especially in those cells with large karyokinetic nuclei ; and frequently a vacuole or 

 basin-shaped space may be seen on the central nuclear heap, the cavity of the vacuole or 

 basin being continuous with, and apparently a bulging of, the perinuclear space. 



Giant cells, together with erythroblasts, are frequently found in the lumen of the 

 larger splenic veins. 



In the Human Spleen the reticulum of the pulp is intermediate in character between 

 that of the Carnivora and that of the Rodentia, and is more like the former than the 

 latter. The cell processes branch more than in any other spleen, and the nuclei are less 

 numerous, because the cell plates that contain them form a comparatively small propor- 

 tion of the whole. The cell plates seem to resemble, more closely than in any other 

 pleen, those of connective tissue corpuscles. 



A striking feature in the stroma is the presence of large numbers of spindle-shaped 

 muscle fibre cells arranged side by side in the form of sheets, not unlike those in the 

 Amphibians' mesentery. The smallest trabeculse, that consist almost entirely of muscle, 



