210 ANATOMY FOB, NUBSES. [CHAP. XVII. 



to execute their work, the accumulation of urea in the system 

 leads to termination of life. Urea is the final product of all 

 proteid substances, and consequently a diet rich in proteids 

 will increase the amount of urea in the system. When the 

 kidneys are disabled, it is customary for physicians to lighten 

 their work as far as possible by regulating the diet. 



Of the salts, chloride of sodium occurs in the largest quan- 

 tity ; it sometimes disappears temporarily from the urine when, 

 in certain inflammatory diseases, it is needed by the blood. 



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 glycosuria. The "casts," 

 which are found in urine in the various forms of Bright's dis- 

 ease, 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 (1.18 to 1.48 litres), or about three pints (1.42 

 litres). 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 discharge of water in the form of 

 sweat is checked ; at the same time the blood-vessels of the kid- 

 neys are dilated, there is a full and rapid stream of blood through 

 the glomeruli, and an increased 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 ordi- 

 nary 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 



