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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



a tuft of blood-vessels, the glonierulus, and an enveloping expansion of the 

 uniferous tubule, the capsule. The glomerulus is a remarkable structure (see 

 Fig. 82, A). It consists of a small afferent artery which after entering the 

 glomerulus breaks up into a number of capillaries, which, though twisted 

 together, do not anastomose. These capillaries unite to form a single efferent 

 vein of a smaller diameter than the afferent artery. The whole structure, 



< D E F G 



FIG. 82. Portions of the various divisions of the uriniferous tubules drawn from sections of human 

 kidney : A, Malpighian body ; x, squainous epithelium lining the capsule and reflected over the glomer- 

 ulus ; y, z, afferent and efferent vessels of the tuft ; e, nuclei of capillaries ; n, constricted neck marking 

 passage of capsule into convoluted tubule ; B, proximal convoluted tubule ; C, irregular tubule ; D and 

 F, spiral tubules ; E, ascending limb of Henle's loop; G, straight collecting tubule (Piersol). 



therefore, is not an ordinary capillary area, but a rete mirabile, and the phys- 

 ical factors are such that within the capillaries of the rete there must be a 

 greatly diminished velocity of the blood-stream owing to the great increase 

 in the width of the stream-bed and a high blood-pressure as compared with 

 ordinary capillaries. Surrounding this glomerulus is the double- walled capsule. 

 One wall of the capsule is closely adherent to the capillaries of the glomerulus; 

 it not only covers the structure closely, but dips into the interior between the 

 small lobules into which the glomerulus is divided. This layer of the capsule 

 is composed of flattened endothelial-like cells, the glomerular epithelium, to 

 which great importance is now attached in the formation of the secretion. It 

 will be noticed that between the interior of the blood-vessels of the glomerulus and 

 the cavity of the capsule which is the beginning of the uriniferous tubule there 

 are interposed only two very thin layers, namely, the epithelium of the capil- 

 lary wall and the glomerular epithelium. The apparatus would seem to afford 

 most favorable conditions for filtration of the liquid parts of the blood. The 

 epithelium clothing the convoluted portions of the tubule, including under this 

 designation the so-called irregular and spiral portions and the loop of Henle, is 

 of a character quite different from that of the glomerular epithelium (Fig. 82, B, 

 C, D, E, F, G). The cells, speaking generally, are cuboidal or cylindrical, proto- 

 plasmic, and granular in appearance; on the side toward the basement mem- 

 brane they often show a peculiar striation, while on the lumen side the extreme 



