642 THE KIDNEYS. 



The structure of these bodies consists of a thick mem- 

 brane of cellular tissue, which surrounds and forms their 

 proper coat, and processes which are traced within, sep- 

 arating its several parts. In the centre a small trian- 

 gular cavity is seen, containing, in the foetus, a viscid 

 reddish fluid ; in the child, a yellow fluid ; in the adult, 

 a dark brown liquid ; while, in old age, it is almost en- 

 tirely empty. 



This cavity is not always found, and by some is denied 

 to exist at all, and when present is attributed either to the 

 enlargement of a vein, decomposition, or laceration. 



The arteries come from the renal, aorta, and phrenic. 



The veins of the right go to the vena cava ascendens ; 

 those of the left enter the emulgent. 



The nerves are from the renal and solar plexus. Each 

 capsule is divided into lobes, and these again have been 

 divided into lobules, having granules, which are found to 

 be connected with the veins. 



Function. The use of the renal capsules is as yet un- 

 known. In the foetus, like the thymus and thyroid bodies, 

 they are large, and are supposed to be connected with 

 foetal sanguification. 



Function of the Kidneys. The use of these glands, it is 

 well known, is to secrete the urine ; and the cortical por- 

 tion of the kidney, which is exceedingly vascular, has 

 been assigned as the especial part where the secretion 

 occurs, while the tubular conveys the fluid down the coni- 

 cal fasciculi to the papilla?, through which it passes into 

 the pelvis. The uriniferous tubes are lined by mucous 

 membrane, and are found by Henle to contain epithelial 

 cells, which, as in other glands, are regarded as the true 

 secreting agents. When filled, they break and discharge 

 into the tubuli uriniferi, others being formed from the 

 nuclei of the extinct cells. 



The urine is composed principally of water. It also 

 contains urea., a substance highly charged with nitrogen, 

 and also lithic or uric acid. In children hippuric acid is 

 found instead of the lithic. Lactic acid, an animal extractive 



