320 THE URINARY APPARATUS 



place by a rise of blood pressure in the arterioles 

 (afferent vessels). The capsule of Bowman becomes 

 so distended that the two layers of cells approximate 

 and practically obliterate the cavity between them. 

 Then the water, salts, sugars, peptones, etc., pass 

 from the blood to the interior of the capsule of Bow- 

 man, by a process of filtration or transudation through 

 the capillary wall and the thin inner layer of Bow- 

 man's capsule, and pass along the tubules. However, 

 Heidenhain believes that the latter constituents of 

 the urine are passed through the glomerular epithe- 

 lium by the processes of cell selection and cell activity; 

 in other words, the entire constituents of the urine 

 obtained in the capsule of Bowman from the blood 

 is due to process of secretion, assisted or regulated by 

 the degrees of blood-pressure, blood-velocity, etc. 



The blood of the glomerulus being emptied of a 

 portion of its water, salts, etc., as described above, 

 still possesses other waste products in the blood 

 which must be eliminated as urea, uric acid, etc. This 

 further elimination is based on a distinct and proved 

 function of the cells, lining the convoluted tubules of 

 the kidney, of selecting from the blood and secreting 

 the above-mentioned products as constituents of the 

 urine. The methods by which these products leave 

 the glomerulus and reach the cells of the convoluted 

 tubules is as follows: A small arteriole leaves each 

 glomerulus (efferent vessel) and divides and sub- 

 divides, forming a capillary net-work, which surrounds 

 the convoluted tubules, thus bringing the blood in 

 intimate relation with the lining cells of the tubules, 

 which, to repeat, select and secrete the urea, uric 

 acid, etc., from the blood, and eliminate them in the 

 urine. 



The remaining quantity of blood which has given 

 off its waste product to be eliminated by the two 

 methods described above, is taken up by venules 

 which anastomose with the arterioles around the con- 



