ACTION OF SALINE DIURETICS 705 



There can be no doubt, however, that vascular changes are 

 not the whole explanation of saline diuresis. For, if they were, 

 the diuresis ought to be equal for all solutions with the same 

 osmotic pressure ; but it is not. When different neutral salts 

 are injected in such quantities that the blood becomes equally 

 diluted, or when solutions isotonic with the blood are used, different 

 degrees of diuresis are produced. Magnus, for instance, found 

 that sodium sulphate is much more diuretic than sodium chloride, 

 although the vascular changes in the two cases were much the 

 same in kind and degree. He considered that the only possible 

 explanation was that the sulphate stimulated the renal cells to 

 greater activity than the chloride, and that the result was a strong 

 confirmation of Heidenhain's view. Cushny has given an explana- 

 tion of these results compatible with Ludwig's view. In this 

 view it is clear that we have to consider as a possible cause of 

 diuresis not only increased filtration, but also decreased absorption 

 by the tubule. He injected equimolecular amounts of chloride 

 and sulphate simultaneously into a rabbit, and found that at 

 the height of the diuresis they were excreted in the urine in 

 approximately the same proportion as they existed in the blood. 

 He looked upon this urine as closely resembling the glomerular 

 filtrate, which he considered was hurried through the tubules too 

 fast for much absorption to take place. As the diuresis passed 

 off he found that the sulphate in the urine predominated over the 

 chloride, although in the blood the reverse was true. He ex- 

 plained this result on the assumption that chloride can permeate 

 the tubule epithelium more readily than sulphate, and is there- 

 fore more readily absorbed, except when the glomerular filtrate 

 is being passed with extreme rapidity down the tubule, as at the 

 height of diuresis. The superior diuretic action of a sulphate is 

 in his opinion due to its less ready absorption ; consequently it 

 opposes a greater osmotic resistance to the absorption of water 

 by the tubule cells, and more fluid is retained in the tubule. He 

 found that phosphates and urea were excreted in the same way 

 as sulphate relatively to chloride, and explained their superior 

 diuretic action accordingly. In order to test this explanation of 

 the different degrees of diuresis produced by various crystalloids, 

 he performed another series of experiments on rabbits. He com- 

 pared the urine obtained from one ureter in which a resistance of 

 15 to 30 mm. Hg was introduced with the urine from the free 



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