THE KIDNEY. 127 



with a certain amount of its water, which passes through the walls of 

 the capillaries and through the cells covering them. Whether this be 

 due to osmosis or to some selective power of the cells we have no 

 concern suffice it that certain salts afterwards appearing in the 

 urine do not leave the blood at this point. The efferent glomerular 

 arteriole, it will be remembered,, breaks into a second capillary plexus, 

 which brings the blood close to the walls of the convoluted tubules. 

 We believe that the cells lining these tubules select from the blood, 

 circulating in the contiguous capillaries, such effete materials as es- 

 caped elimination from the glomeruli. Moreover, that some of the 

 water, together with serum albumin, which escaped in the first in- 

 stance and entered the proximal convoluted tubules, is here returned 

 to the blood by the intervention of the same tubular lining cells 

 which excrete the salts. That in the cells of these tubules there 

 exist currents in opposite direction one from the intertubular 

 capillaries into the proximal part of the tubule; and one from the 

 dilute urine in the tubule into the capillaries. Without referring 

 to any further work on the part of the kidney, I wish to impress this 

 part of the structual scheme : That the first part of the uriniferous 

 tubule is the prominent excreting part. That the latter portion of 

 the tubule the portion in the Malpighian pyramids, the straight 

 tubule is for the collection and drainage of the urine already ex- 

 creted. And that between the excreting first part and the draining 

 second part, there exists a narrow looped tubule the loop of Henle. 

 The effect of this narrowing and tortuosity of the tubule will be to 

 present a resistance to the outflow of urine from the proximal portion 

 of the tubule. The dilute urine, excreted in the Malpighian bodies, 

 is held back for awhile in the proximal convoluted, and time given 

 for the completion and perfection of the excretory processes by the 

 tubular parenchyma. 



PKACTICAL DEMONSTRATION. 



The human kidney is rarely found in a perfectly normal condition. 

 The demonstration can be made from the kidney of the pig, except 

 as regards certain features. The medullary pyramids do not exist in 

 the domestic animals, and the parenchyma presents very essential 

 differences from the cells of the human kidney. Still, very much 

 can be learned from the organ of the pig, dog, and rabbit. The tis- 

 sue should be divided so as to permit sections to be made parallel 

 with the medulla, and to include both it and the cortex. The hard- 

 ening is best by Miiller's fluid. Small pieces hardened quickly in 

 strong alcohol, however, stain very finely with haema. and eosin. 

 Very pleasing differentiation may also be secured by staining slowly 



