THE SPLEEN. 



1079 



or reddish-yellow granules of various sizes which present the characters of the 

 haematin of^the blood. Sometimes, also, unchanged blood-disks are seen included 

 in these cells, but more frequently blood-disks are found which are altered both 

 in form and color. In fact, blood-corpuscles in all stages of disintegration may 

 be noticed to occur within them. Klein has recently pointed out that some- 

 times these cells in the young spleen contain a proliferating nucleus ; that is to 

 say. the nucleus is of large size, and presents a number of knob-like projections, 

 as if small nuclei were budding from it by a process of gemmation. This observa- 

 tion is of importance, as it may explain one possible source of the colorless blood- 

 corpuscles. 



The interspaces or areolne formed by the framework of the spleen are thus filled 

 by a delicate reticulum of branched connective-tissue corpuscles the interstices of 

 which are occupied by blood, and in which the blood-vessels terminate in the 

 manner now to be described. 



Blood-vessels of the Spleen. The splenic artery is remarkable for its large 

 size in proportion to the size of the organ, and also for its tortuous course. 



FIG. 689. Transverse section of the human spleen, showing the distribution of the splenic artery and its 

 branches. 



It divides into twelve to fifteen branches, which enter the hilus of the spleen 

 and ramify throughout its substance (Fig. 689), receiving sheaths from an 

 involution of the external fibrous tissue. Similar sheaths also invest the nerves 

 and veins. 



Each branch runs in the transverse axis of the organ from within outward, 

 diminishing in size during its transit, and giving off in its passage smaller 

 branches, some of which pass to the anterior, others to the posterior part. These 

 ultimately leave the trabecular sheaths, and terminate in the proper substance of 

 the spleen in small tufts or pencils of minute arterioles, which open into the 

 interstices of the reticulum formed by the branched sustentacular cells. Each of 

 the larger branches of the artery supplies chiefly that region of the organ in 

 which the branch ramifies, having no anastomosis with the majority of the other 

 branches. 



The arterioles, supported by the minute trabeculae. traverse the pulp in 

 all directions in bundles or penicilli of straight vessels. Their external coat, on 

 leaving the trabecular sheaths, consists of ordinary connective tissue, but it gradu- 

 ally undergoes a transformation, becomes much thickened, and is converted into 

 a lymphoid material. 1 This change is effected by the conversion of the con- 

 nective tissue into a cystogenous tissue, the bundles of connective tissue becoming 



1 According to Klein, it is the sheath of the small vessel which undergoes this transformation, 

 and forms a " solid mass of adenoid tissue which surrounds the vessel like a cylindrical sheath " (Atlas 

 of Hisloloyy, p. 



