THE RENAL SECRETION. 



into the renal vein. Most of the blood flowing through the- 

 kidney thus goes through two sets of capillaries; one in the 

 capsules, and a second formed 

 by the breaking up of the 

 efferent vein of the latter. 

 The capillary network in the 

 pyramids is much less close 

 than that in the cortex, which 

 gives reason to suspect that 

 most of the secretory work of 

 the kidneys is done in the cap- 

 sules and convoluted tubules. 

 The pyramidal blood flows 

 only through one set of capil- 

 laries, there being no glome- 

 ruli in the kidney medulla. 



The Renal Secretion. The 

 amount of this carried off 

 from the Body in 24 hours is 

 subject to considerable varia- 

 tion, being especially dimin- 

 ished by anything which pro- 

 motes perspiration, and increased by conditions, as cold to 

 the surface, which diminish the skin excretion. Its average 

 daily quantity varies from 1200 to 1750 cub. cent. (40 

 to 60 fluid ounces). The urine is a clear amber-colored 

 liquid, of a slightly acid reaction; its specific gravity is 

 about 1022, being higher when the total quantity excreted 

 is small than when it is greater, since the amount of solids 

 dissolved in it remains nearly the same in health; the 

 changes in its bulk being dependent mainly on changes 

 in the amount of water separated from the blood by the 

 kidneys. 



Normal urine consists, in 1000 parts, of about 960 water 

 and 40 solids. The latter are mainly crystalline nitro- 

 genous bodies (urea and uric acid), but small quantities of 

 pigments and of non- nitrogenous organic bodies are also 

 present, and a considerable quantity of mineral salts. The 

 following table gives approximately, in the first column, the 



./i 



FIG. 116. The termination of a, 

 uriniferous tubule, with its glomeru- 

 lus. a, theglomerulusorMalphighian 

 corpuscle; 6, the convoluted ending 

 of the tubule: d, its lining epithelium? 

 /, the afferent blood-vessel of the 



flomerulus ; g, the efferent vessel ; c, 

 , the blood-vessels forming the tuft 

 in the glomerulus. 



