THE REACTION OF THE URINE 725 



tubules the red colour appeared both in the lumen and in the 

 cells lining it. There can be no doubt, therefore, that the 

 glomerular nitrate is alkaline and becomes acid in the convoluted 

 tubules. And this conclusion is supported by the observation 

 that diuresis decreases the acidity of the urine, and that this 

 decrease is proportional to the degree of diuresis, no matter how 

 the increased flow of urine is brought about. 



We have now to inquire into the mechanism by which this 

 change in reaction is brought about. It is clear that the alkaline 

 glomerular filtrate might be made acid in the tubule either by the 

 absorption of bases or by the excretion of acids. Dreser tried to 

 prove that the change in reaction was brought about by a process 

 of excretion. He injected acid fuchsin into frogs ligatured by 

 Nussbaum's method, and found that the red colour could still be 

 seen in the convoluted tubules. But, in the absence of evidence 

 that the glomeruli were wholly out of circulation, this conclusion 

 cannot be accepted. Liebermann put forward a view to explain 

 how the tubule cells could excrete acid salts although they receive 

 only alkaline ones from the blood. He separated from the kidney 

 a lecith-albumen capable of combining with bases, so that it 

 would convert a neutral or alkaline phosphate into the acid salt. 

 He found that the neutral combination of lecith-albumen with 

 base would give up its base to C0 2 and become again capable of 

 uniting with fresh base. He imagined that the following alterna- 

 tion of changes went on during the secretion of urine firstly, 

 base was taken from the blood phosphates and the acid radicles 

 passed into the urine, and then the base remaining behind in the 

 cell, in combination with the lecith-albumen, was taken up by 

 C0. 2 and passed into the venous blood as carbonate. Such a 

 transference of base from phosphate to carbonate could not take 

 place unless the mass influence of the two acids were rapidly 

 alternating backwards and forwards, but there is no obvious 

 reason why they should. 



Before attempting to explain the change in reaction between 

 the blood and urine, it is necessary to inquire into the real extent 

 of the change. This can be done by comparing the reactions of 

 both fluids with indicators whose acid radicle or anion have 

 different strengths of affinity for base or cation. Cushny has 

 pointed out that both blood and urine are acid to phenol-phthalein 

 and alkaline to methyl-orange, but to litmus blood is alkaline 

 and normal urine acid. The alkalinity of the blood to litmus 



