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SCIENCE. 



[N. S. Vol. XXII. No. 569. 



ney. Gottlieb and Magnus, therefore, felt 

 justified in concluding that the increased 

 blood flow through the kidney is not the 

 primary and determining condition for in- 

 creased diuresis, but rather a regular and 

 not essential associated phenomenon. My 

 collaborator, Professor Loewi, also carried 

 on a large number of experiments in this 

 direction. He, too, found that in certain 

 cases the oncometer showed no increase in 

 the volume of the kidney, notwithstanding 

 an increase in diuresis. We further un- 

 dertook to determine whether diuresis oc- 

 curred under the influence of diuretic 

 agents, like caffeine and salts, even when 

 the volume of the kidney was fixed so that 

 an increased blood flow is presumably pre- 

 vented. For this purpose the left kidney 

 of the rabbit in a relatively quiescent and 

 relatively anemic condition was encased in 

 plaster of Paris with the exception of the 

 hilus only, so that an increase in the volume 

 of the kidney was wholly excluded. The 

 surprising result was obtained that even 

 in the case of such rigidly enclosed kidneys, 

 diuretics like caffeine and salts were able 

 to induce an abundant diuresis. Hence it 

 seemed to be actually true that an increased 

 filtration may be induced without any in- 

 crease in the blood flow through the kid- 

 neys. But more careful investigations 

 showed that the volume of the kidney is by 

 no means a certain measure of the blood 

 flow through this organ, but that the vol- 

 ume of the kidney and the blood flow 

 through it may be independent. For by 

 inspection of the outflowing venous blood 

 it could be seen that, notwithstanding the 

 rigid limitation in the volume of the kid- 

 ney, the flow of blood through the organ 

 was always enhanced during diuresis. 

 While the blood which flowed through the 

 renal vein was dark previous to the diuresis, 

 the stream took on a light, arterial color 

 under the influence of caffeine and salts. 



The mere fact, therefore, that the kidney 

 does not increase in size in some cases of 

 caffeine diuresis is no proof that the proc- 

 ess of diuresis does not depend on an in- 

 creased flow of blood through the kidney, 

 and one may say that an increased renal 

 blood flow is a regular and essential condi- 

 tion of diuresis from salts, urea and caf- 

 feine — a condition wholly sufficient, in it- 

 self, to explain the diuresis. It is not pos- 

 sible to say with certainty whether in the 

 case of caffeine diuresis there is also a dim- 

 inished resorption of fluid through the 

 urinary tubules, as Sobieranski 's experi- 

 ments appeared to show. Another impor- 

 tant fact was brought out by Loewi in this 

 connection; we know that every hydremia, 

 whether induced by the administration of 

 water or by the withdrawal of water from 

 the tissues by means of salts intravenously 

 injected, gives rise to an increased diuresis, 

 without any increase in the general blood 

 pressure or the work of the heart. What 

 is the origin of such a diuresis? Loewi 

 found that every hydremia, whatever may 

 be its origin, acts upon the vessels of the 

 kidney as a specific excitant, in that it 

 dilates the vessels and thus causes an in- 

 creased glomerular filtration. Thus we 

 have obtained an explanation for the in- 

 creased secretion of urine arising from all 

 forms of hydremia, from the drinking of 

 water, and from the withdrawal of water 

 from the tissues, in consequence of the 

 action of the diuretic salts. Hence we may 

 say that all the observations that have come 

 to us by physiological and pharmacological 

 methods harmonize with the conception 

 that the water of the blood and the free 

 crystalloids therein dissolved are liberated 

 from the glomeruli by the process of filtra- 

 tion or perhaps a process better described 

 as transudation, and, further, that the 

 urinary tubules reabsorb, by means of their 

 epithelial cells, not only water, but also, in 



