STRUCTURES AND PROCESSES OF OBSCURE NATURE. 469 



ing as they go both capsule and cortex with a moderate number of vessels, 

 end in the medulla the connective-tissue bars of which bear numerous large 

 venous sinuses, into which the capillaries pour their blood, and from which 

 the blood is gathered up into the supra-renal vein. 



A large number of nerves, consisting chiefly of medullated fibres from 

 the solar plexus, the renal plexus, the phrenic nerve, and the vagus, pass 

 into the supra-renal body at the hilus and on the under surface, and forming 

 numerous plexuses, coarse and fine, some carrying small groups of nerve 

 cells, end chiefly in the medulla, though some pass on to the cortex. The 

 ultimate endings are not yet known. 



The lymphatics are fairly numerous, and form plexuses in the capsule 

 and in the connective tissue of the framework ; it is stated that the lym- 

 phatic vessels surrounding the groups of cells in the cortex communicate 

 with spaces between the cells. 



412. Besides the ordinary proteid and other chemical constituents, the 

 supra-renal body contains some substance or substances possessing striking 

 color reactions, giving a dark-blue or dark-green color with ferric chloride, 

 and a carmine-red tint with various oxidizing agents. This substance (whose 

 nature is not exactly known, and which is confined to or most abundant in 

 the medulla) is not soluble in the ordinary solvents of pigments, such as 

 alcohol, ether, chloroform, etc., but is readily soluble in dilute acids. 



Among the extractives, hippuric and benzoic acid, and taurocholic acid 

 or taurin have been found, but it is not certain that these are normal con- 

 stituents. 



413. Some of the histological features of the supra-renal bodies, 

 namely, the groups of cells and their abundant blood-supply, suggest, on 

 the one hand, that important metabolic processes take place in them, some 

 of which are probably connected with the history of the pigments of the 

 body at large. On the other hand, the unusually large nerve-supply, and 

 the derivation of part of the body from the sympathetic ganglia, suggest 

 peculiar nervous connections. And the organ has often served as a starting- 

 point for speculations in these two directions ; but our exact knowledge con- 

 cerning them is very limited. The results of experiment have taught us 

 little ; extirpation, for example, has been often followed by the death of the 

 animal operated upon, but the cause of the death in such cases is by no 

 means clear. 



One fact, gained by clinical experience, is the only real item of know- 

 ledge which we possess. Disease of the supra-renal bodies, apparently 

 tubercular in nature and beginning in the medulla, is so often associated 

 with a change in the color or with an increase of the pigment of the skin 

 " bronzed skin," " Addison's disease " that some connection between the two 

 must exist; but the several links of the chain are as yet unknown. It is 

 tempting to associate the increase of pigment in the bronzed skin with the 

 chromogen or color-yielding substance spoken of above; but we have no 

 warrant for doing so, such, for instance, as any indication of ties between 

 the supra-renal bodies and changes either in haemoglobin itself or in bilirubin, 

 which two bodies we have reason to regard more particularly as mothers of 

 pigment. Moreover the bronzed skin is only one of the symptoms of Addi- 

 son's disease, failure of nutrition and nervous symptoms being also present. 



414. The thymus. This, though it arises in the embryo as a paired 

 outgrowth from the epithelial walls of a pair of visceral clefts, and thus 

 begins as an epithelial structure into which mesoblastic elements subse- 

 quently intrude, soon puts on such characters as to appear essentially a 

 lymphatic structure, and, indeed, might be regarded as a part of the lymph- 

 atic system. 



