392 STUDIES IN ADVANCED PHYSIOLOGY. 



of the Malpighian corpuscles of the cortex as mechanical 

 rather than physiological, serving merely as flush basins at 

 the top of the tubule to keep this lumen perfectly clear of 

 obstructions, while the cells that line the tubule are the 

 physiological agents directly concerned in picking out of the 

 blood the waste products in question. 



It may be well to repeat at this point the fact that these 

 nitrogenous products are not formed by the kidney at all. 

 Derived in the form of kreatin or kreatinin, or similar sub- 

 stances from the breaking down of the tissues, they are car- 

 ried to the liver and there changed to urea and its kindred 

 compounds, from which place by means of the regular blood 

 stream they reach the kidney, and in this organ are merely 

 picked up by the tubular epithelium and eliminated. It 

 must not, however, be supposed that this elimination of the 

 nitrogenous products is a mere physical filtration. It is an 

 active physiological process, depending upon the vital 

 energy of the epithelial cells that line the tubules. It is due 

 to the special activity of these cells that these waste pro- 

 ducts are removed, and that many other almost equally di- 

 alyzable substances are not permitted to pass through. In 

 cases of inflammation, or in cases of the more or less gen- 

 eral disintegration of these epithelial cells, other substances 

 do pass into the secretion and such diseases as diabetes or 

 Bright 's disease are the result. 



The elimination of the water and salt in the glomeruli 

 or the Malpighian corpuscles, is to a very large extent a 

 physical process. This is proved by the fact that the amount 

 of such water and salt eliminated from the kidney is to some 

 extent directly proportional to the amount of blood which 

 passes through the kidney and to the arterial pressure in the 

 kidney, hence any rise in arterial pressure or any increase 

 in the swiftness of the blood stream will usually reveal itself 

 in an increased secretion from that organ. That it is 

 nothing but a physical filtration is not claimed. In fact, it 

 is probable that even the lining cells of the corpuscle exert 

 a physiological action. 



