URINE 



183 



and leave the kidney by a course parallel to that of the 

 entering arteries. 



4. The Composition of Urine and Chemistry of 

 Urea. — The renal secretion is a clear yellowish tluid, 



Fig. 5f>. — BLfioD Vessels of Kidkey. (Cadiat.) 



a, part of arterial arch ; 6, interlobular artery ; c, glomerulus ; d, 

 ferent vessel ; e, capillaries of cortex ; f, small arteries of raedulla ; 

 g, venous arch ; k, straight veins of medulla ; i, interlobular vein. 



whose specific gravity is not very different from that of 

 blood-serum, being 1-020. In health it has a slightly 

 acid reaction, due to the presence of acid sodium phos- 

 phate. It is composed chiefly of water, holding in solu- 

 tion (i) organic substances, of which the chief is urea. 



