REACTION OF THE URINE. 657 



state of extreme emaciation. This latter result is difficult to explain, 

 and will be discussed in another section of this volume. The former 

 result (the hydruria) may, however, be analogous to the results of 

 Ribbert's experiments, and may be due to a diminution in the actively 

 absorbing or secretory mechanisms of the kidney, i.e. the convoluted 

 tubules. It seems probable that a deficiency in the excretory powers of 

 the organism could be more easily compensated by augmenting the 

 glomerular transudation by means of the blood supply to the glomeruli, 

 than by increasing the work of the cells of the convoluted tubules. t 



Arguments based upon the reaction of urine. An objection which has 

 been frequently urged against the filtration hypothesis is that, whereas 

 the blood serum or plasma is in all animals alkaline, the urine, except in 

 those cases where there is a rich supply of alkali in the food, is acid 

 in reaction. It seems difficult to conceive how a process of filtration 

 could effect this change in the reaction of the filtrate. Since all author- 

 ities are agreed that the urine undergoes changes in composition on its 

 way through the tubules, it becomes important to find out whether the 

 urine, as it is formed by the glomeruli, is alkaline or acid. 



Dreser 1 has sought to determine this question by examining the 

 microchemical reactions in the different parts of the kidney in the frog. 

 As his indicator he used acid fuchsin (rubin S.) This substance is a 

 brilliant red in acid solutions, but is almost colourless in weak alkaline 

 solutions. It is, therefore, a convenient substance to use in order to 

 demonstrate the formation of acid in muscle during tetanus. A strong 

 solution of this dye was injected into the dorsal lymph sac of the frog. 

 An hour or two later the urine that was secreted was of a deep red 

 colour, and was acid in reaction. On examining the kidneys, the dorsal 

 part in which the glomeruli are situated was found to be colourless, but 

 the tubules in the ventral part were filled with red secretion. If the 

 injection were repeated the red coloration extended to the lining cells 

 of the tubules. From his experiments with this and other dyes, Dreser 

 concludes that the production of the acid reaction is effected by the cells 

 of the convoluted tubules, and that the glomerular transudate is alkaline. 



This conclusion is borne out by the results of injecting any kind of 

 diuretic. If the glomerular transudate is alkaline, and is also rendered 

 acid in its passage through the tubules, we should expect that the more 

 abundant the glomerular transudate, the shorter would be the time taken 

 in its passage through the tubules, so that the urine pouring into the 

 bladder would tend to approximate in reaction and composition the 

 original glomerular transudate. Such is found to be the case. Whatever 

 means we use to induce profuse diuresis, whether by the injection or 

 administration of drugs such as caffein or theobromin, or the adminis- 

 tration of saline diuretics, or the production of hydraemic plethora, 

 we find that the acid reaction of the urine disappears, to be replaced by 

 a neutral or alkaline reaction. We may conclude, with a high degree of 

 probability, that the glomerular part of the urinary secretion is alkaline 

 in reaction, and that the acid reaction of the urine of carnivora or 

 of starving herbivora is due to the changes wrought on the glomerular 

 transudate by the cells of the convoluted tubules. Whether this 

 change is due to the secretion of acid salts, or to the absorption of 

 alkaline salts by the cells of the tubules, we are not in a position to 

 determine. 



1 Ztschr.f. Bid., Munchen, 1885, Bd. xxi. S. 41. 

 VOL. l. 42 



