NOVEMBEK 24, 1905.] 



SCIENCE. 



657 



blood, which can not transude or filter 

 through the normal glomeruli are not 

 driven through with the water flow. They 

 must rather be secreted through specific 

 cell activity and quite independently of all 

 mechanical filtration. 



Indeed, we have known for a long time, 

 from purely clinical observations, that 

 some urinary constituents, like urea and 

 sodium chloride, are excreted almost pro- 

 portionately to the volume of the urine; 

 and that others, on the contrary, like uric 

 acid and phosphoric acid, are not influ- 

 enced by the quantity of urine. In order 

 to examine this problem in a quantitative 

 way, a series of observations has been 

 made by my assistant and collaborator, 

 Otto Loewi. These experiments were made 

 on dogs and rabbits in the following man- 

 ner: The normal excretion of uric acid, 

 urea and phosphoric acid was studied dur- 

 ing a preliminary period of several hours. 

 In still other cases the excretion of sugar 

 was studied — indeed, not merely in dia- 

 betes following pancreas extirpation, but 

 also after phlorhizin administration and 

 intravenous injections of sugar. Then the 

 secretion of urine was increased experi- 

 mentally through free administration of 

 water or by means of diuretics, such as 

 sodium nitrate or caffeine, and during the 

 diuresis so induced the above-mentioned 

 constituents were quantitatively deter- 

 mined. Finally similar observations were 

 made during and after the period following 

 the cessation of the diuresis. The outcome 

 was that the excretion of urea and of 

 chlorides ran regularly parallel with the 

 volume of the urine. On the other hand, 

 there was never observed any parallelism 

 between the excretion of water, on the one 

 hand, and the increased amount of uric 

 acid and phosphoric acid normally pro- 

 duced in the organism, on the other. I 

 specially emDhasize the phosphoric acid 



normally produced in the organism, for 

 any phosphoric acid introduced as a salt 

 into the circulation showed a different be- 

 havior. Such introduced salts followed 

 the same law of excretion as the chloride 

 and urea; and this same general law held 

 true in the case of sugar. ' 



The blood, as is well known, always con- 

 tains sugar, but in a combined form, so 

 that the sugar under normal conditions is 

 not excreted by the kidneys. But after 

 pancreas extirpation or after an intraven- 

 ous infusion of sugar in normal animals, 

 the sugar content of the blood rises above 

 the normal; the greater part of it can not 

 exist in combination in the blood but is 

 free and, like urea and other crystalloids, 

 is excreted by the urine. And it appears 

 from Loewi 's experiments on diuresis that 

 in such pancreatic or infusion diabetes, the 

 quantity of excreted sugar was always pro- 

 portional to the volume of urine excreted. 

 In phlorhizin diabetes, on the other hand, 

 the behavior was entirely different. As 

 you are aware, there occurs no hypergly- 

 caemia in phlorhizin glycosuria. There is 

 no increase of free sugar in the blood, but 

 the normally combined sugar is liberated 

 from its combination and excreted from the 

 kidneys. And this specific cellular sugar 

 excretion was shown to be quite indepen- 

 dent of the filtration of fluid through the 

 glomeruli, that is independent of the 

 amount of diuresis. From this it seems to 

 follow, in fact, that the substances which 

 exist free in the blood pass out mechanic- 

 ally with the water; while other bodies, 

 such as uric acid, phosphoric acid, phlor- 

 hizin-sugar, and probably the urinary pig- 

 ments, are excreted from the kidney by 

 special. secretory activity. It is not neces- 

 sary that a substance exist in a crystalline 

 state in order that it be secreted by mech- 

 anical filtration through the glomeruli ;- it 

 may equally well be a colloid, provided. 



