254 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



one depending upon the living structure and properties of the epithelial cells. 

 In support of this view he quotes the fact that partial compression of the 

 renal veins quickly slows or stops altogether the flow of urine. Compression 

 of the veins should raise the pressure within the vessels of the glomeruli, and 

 upon the filtration hypothesis should increase rather than diminish the secre- 

 tion. It has been shown also that if the renal artery is compressed for a 

 short time so as to completely shut off the blood-flow to the kidney the 

 secretion is not only suspended during the closure of the arteries but for a 

 long lime after the circulation is re-established. According to Tiegerstedt, 

 if the renal artery is ligated for only half a minute the activity of the 

 kidney is suspended for three-quarters of an hour. This fact is difficult to 

 understand if the glomerular epithelium is regarded simply as a filtering mem- 

 brane, but it is explicable upon the hypothesis that the epithelial cells are 

 actively concerned in the production of the water. 



The uncertainty as to the mechanism of production of the water and salts 

 renders it difficult to give a theoretical explanation of the action of diuretics. 

 V T arious -aline substances, such as NaCl and KXO s , increase the flow of urine. 

 According to Starling, 1 these substances increase the bulk of water in the 

 blood by drawing water from the tissues. A condition of hydraemic plethora. 

 ensues, causing a greater volume of blood in the kidney capillaries and a rise 

 of capillary pressure, conditions that favor greater filtration and account in 

 part for the increased amount of urine. Experiments seem to show, however, 

 that the condition of hydraemic plethora passes off before the increased secre- 

 tion of urine ceases, so that the diuretic action of the salts is not due to this 

 factor alone. The adherents of the filtration theory assume that in addition 

 the -alts cause a vaso-dilatation in the kidney, and thus produce a rise in 

 blood-pressure in the glomeruli. According to the other point of view, these 

 substances may be considered as having a specific stimulating effect upon the 

 glomerular epithelium. So the action of caffein may be referred either to a 

 specific action- on the secreting cells or possibly to an indirect effect exerted 

 through the circulation of the kidney. It seems clear that at present we arc 

 not justified in asserting more than that the glomeruli control in some way the 

 production of the water and salts of the secretion. The extent of the activity 

 seems to be correlated with the quantity of blood flowing through the 

 glomeruli. 



It must be borne in mind, however, that some water and probably also 

 some of the inorganic salts are secreted at other part- of the tubule along 

 with the nitrogenous wastes. It is of interest to add that the most important 

 of the abnormal constituents of the urine under pathological conditions, such 

 as the albumin in albuminuria, the haemoglobin in haemoglobinuria, and the 

 sugar in glycosuria, seem likewise to escape from the blood into the kidney 

 tubule- through the glomerular epithelium. 



1 Journal of Physiology, 1899, vol. 24, i>. :!17. 



Von Schr ler : Archiv. fur exper. Pathologie and Pharmakol ., Bd. xxiv. S. 85; and 



Dreser, Ibid., 1892, Bd. xxix. S. 303. 



