CHAP. XVI.] ELIMINATION. 187 



The chief abnormal constituents that are liable to appear in 

 the urine are albumin, giving rise to a condition called albu- 

 minuria, and sugar, giving rise to diabetes. The " casts," which 

 are found in urine in the various forms of Blight's disease, are 

 shed from the tubules in the shape of cylindrical moulds. 



The quantity of urine passed in twenty-four hours. The normal 

 quantity of urine passed in twenty-four hours is from forty to 

 fifty ounces, or about three pints. This will vary in health 

 with the condition of the skin, and the amount of fluid taken 

 into the body. The excretion of water by the kidneys is closely 

 related to that excreted by the skin. When the body is exposed 

 to cold, the blood-vessels in the skin are constricted, and the dis- 

 charge of water in the form of sweat is checked ; at the same 

 time the blood-vessels of the kidneys are dilated, there is a full 

 and rapid stream of blood through the glomeruli, and an in- 

 creased flow of urine results. On the other hand, when the 

 body is exposed to warmth, the cutaneous vessels are widely 

 dilated, and the skin perspires freely, while the renal vessels being 

 constricted, only a small and slow stream of blood trickles 

 through the glomeruli, and the urine which is secreted is 

 scanty. The effect on secretion, however, is more marked by 

 the amount of fluid absorbed through the alimentary canal ; an 

 increased secretion of water always follows an ordinary meal, 

 and when large quantities of water are drunk the amount of 

 urine is correspondingly increased. 



The supra-renal capsules. Lying immediately above each kid- 

 ney are two small flattened bodies of a yellowish colour. They 

 are usually classified with the ductless glands, as they have no 

 excretory duct. Each organ is invested by a fibrous capsule 

 which sends fibres into the glandular substance; these fibres 

 form a framework for the soft, pulpy substance of the gland, 

 and within the spaces of the framework are groups of cells. 



The supra-renal capsules are plentifully supplied with blood- 

 vessels, nerves, and lymphatics, and they contain some striking 

 colouring matters. In disease of these organs, the skin fre- 

 quently becomes " bronzed," from an increase of pigment or 

 colouring matter. Their special normal functions are unknown. 



