388 STUDIES IN ADVANCED PHYSIOLOGY. 



All the points so far could easily be made out on a kid- 

 ney without the use of any -lens. For the final structure, 

 the courses of the blood-vessels and the uriniferous tubules, 

 recourse must be had to histological sections. For the sake 

 of clearness it may be advisable to follow at first the course 

 of the blood-vessels for some distance without paying atten- 

 tion to other structures, and then to turn to the uriniferous 

 tubules. 



1. The Circulation of Blood Through the Kidneys. 

 The renal artery enters the kidney at the hilum, and at once 

 divides into numerous branches which run in every direc- 

 tion between the cortex and the medulla. From these main 

 branches there arise smaller ones, which run directly out- 

 wards through the cortex to the capsule. These branches 

 in turn divide into shorter branches, and these short 

 branches soon terminate each in a small knot of blood- 

 vessels, giving to the whole the appearance of a bunch of 

 grapes. This network of blood-vessels is not really a 

 capillary network. It is rather a nodule of small twisted 

 arteries, with walls, however, sufficiently thin to allow the 

 water and the salt of the circulating blood to pass out at 

 this point somewhat readily. It is, therefore, well to bear 

 in mind that the blood as it re-issues from this knot is still 



Fig. 129. A, SHOWING THE RELATIONS OF THE BLOOD-VESSELS AND URINIFEROUS TU- 

 BULE; B, A SINGLE GLOMERULUS FROM A PIG'S KIDNEY. (After Bowman and Lud- 

 wig.) 



arterial. Upon leaving this knot, called a Malpighian cor- 

 puscle or glomerulus, the artery soon divides into capillar- 



