88 PRACTICAL HISTOLOGY. 



outwards between the pyramids of Ferrein. As the interlobular arteries proceed outwards, 

 they give off on all sides small, short trunks the afferent arteries to the Malpighian 

 corpuscles, which they enter and split up into capillaries to form the glomerulus (p. 85). 

 Trace an efferent vessel venous vessel emerging from the capsule at that part where the 

 afferent vessel enters it. The efferent vessel on its exit splits up into capillaries, which form 

 a dense network over and around all the convoluted tubules. From this network the renal 

 vein proceeds. Branches of it will be found accompanying the interlobular arteries. Note at 

 the innermost part of the cortex bunches of vessels, most of which spring from the renal 

 artery and run down in groups into the medulla the vasa recta - where they split up into a 

 network with large oblong meshes surrounding the straight tubules. The medulla is not 

 nearly so vascular as the cortex, but the capillaries of the one are continuous with those of 

 the other (PI. XX., Fig. 3). 



FRESH KIDNEY. 



Make a longitudinal section of a perfectly fresh sheep's kidney. With the naked eye 

 observe the capsule and its loose attachment to the parenchyma. Note the division of this 

 latter into three zones (p. 85) the cortex, boundary, and papillary portion. Study the naked- 

 eye characters of each part. The papillary portion is uniformly vertically striated, due to the 

 straight tubules and blood-vessels running straight towards the apex of the pyramid. The 

 boundary-layer is also striated longitudinally, but is marked by alternate opaque and light 

 bluish-coloured zones ; the former are the continuations of the straight tubules towards the 

 cortex, whilst the latter are due to the vasa recta (p. 88). The cortex is of a light brown 

 colour, and is finely granular in appearance. 



It is important in a human kidney to note the relative thickness of these various parts. 

 If the vertical diameter of the cortex and medulla together be represented by 10, the relative 

 proportions of these three zones from without inwards will be 3^5 : 2'5 : 4 (Klein). The 

 medulla, therefore, is nearly twice as thick as the cortex. 



EXAMINATION (L). Scrape off a small piece of the cortex, and tease it in salt solution 

 with needles. Observe the convoluted tubules with their cloudy epithelium, their nuclei being 

 scarcely visible. Notice especially their basement-membranes, which may be seen in great 

 numbers in the field as fine transparent membranes, often with folds in them. Study them 

 also with (H). Select a glomerulus and study it. Add dilute acetic acid, and observe the 

 effect on the epithelium of the convoluted tubule, in rendering it clear and transparent and 

 revealing a nucleus, and also its effect on the glomerulus in rendering its capillaries clear and 

 transparent, and bringing into view their nuclei. 



Scrape also the medulla, and examine it in the same way (L and H). Note the straight 

 tubules with their well-defined, clear, epithelial cells. Perhaps isolated portions of the looped 

 tubules of Henle may be obtained. 



THE URETER. 



PREPARATION. Tie one end of the ureter of a dog or cat, and slightly distend it with the 

 chromic acid and spirit mixture, then tie the other end ; leave it for two days in the mixture ; 

 then cut it into pieces an inch long, and harden it for two days longer, and complete the 

 hardening in spirit. Make transverse sections, and stain some with logwood, and mount them 

 in dammar. 



