STRUCTURE AND FUNCTIONS OF THE SPLEEN. 289 



are destitute of that system, although the distensible collated cavities, 

 apparently destined to perform its safety-valve function, exist in some 

 of the higher among them. This is an additional reason for regarding 

 its parenchymatous portion as essentially a part of the assimilating ap- 

 paratus of the Absorbent system. 



509. It would further seem as if the Spleen were specially concerned 

 in the development of the red corpuscles of the blood ; since its paren- 

 chyma contains cells which resemble these in various stages of develop- 

 ment. But this organ also appears to promote the disintegration of 

 those red corpuscles which have become effete ; and this so powerfully, 

 that the blood of the splenic vein contains a far less proportion of red 

 corpuscles, and a far greater proportion of albumen, than that of any 

 other vessels in the body. It is supposed by Prof. Kolliker, that the 

 dissolved blood-corpuscles are subservient "to the formation of bile ; the 

 colouring matter of which is nearly allied to that of the blood. 



510. The, Supra-Renal Capsules seem to correspond with the Spleen 

 in their essential structure, w r hilst in the arrangement of their compo- 

 nent parts, they bear more resemblance to the Kidney. Their exterior 

 or cortical portion, in Man and the Mammalia generally, is formed of 

 straight arteries, which divide into a minute capillary network ; and 

 from this arise venous branches, which form a minute plexus through 

 the internal or medullary substance, pouring its contents into a large 

 central cavity, which is the dilated commencement of the supra-renal 

 vein. In the lower Vertebrata, however, there is no distinction of cor- 

 tical and medullary substance ; the distribution of vessels being nearly 

 the same throughout. As in the Spleen, we find in the interspaces of 

 the vascular plexus a parenchymatous structure ; partly composed of 

 free cells and nuclei in various stages of development ; and partly con- 

 sisting of closed granular vesicles, within which similar cells and nuclei 

 are included. There is ground for asserting that these vesicles are 

 themselves at first in the condition of simple cells, and that the cells 

 which they include are a secondary product. In Man and the Mam- 

 malia, these vessels are confined to the cortical substance, and have the 

 form of elongated tubes, lying between its parallel blood-vessels. Thus, 

 then, the supra-renal capsules possess the essential structure of a gland, 

 in every respect save the want of an excretory duct ; and whatever may 

 be the product of their cell action, this must be received back into the 

 blood again. The fluid contents of these bodies/ are rich in proteine 

 compounds and in fat ; and it can be scarcely doubted that these mate- 

 rials here undergo an elaboration, which renders them better fitted for 

 the nutrition of the system. It does not seem unlikely that these bodies, 

 like the Spleen, have a double function ; and that, besides participating 

 in the general actions of the Absorbent glandulse, they may serve as a 

 diverticulum for the Renal circulation, when from any cause the se- 

 creting function of the Kidneys is retarded or checked, and the move- 

 ment of blood through them is stagnated. The Supra-Renal capsules 

 of Man attain a very large size early in foetal life, surpassing the true 

 Kidneys in dimension up to the tenth or twelfth week ; but they after- 

 wards diminish relatively to the latter, and are evidently subordinate 

 organs during the whole remainder of life. In most of the lower ani- 



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