RE A CTION OF THE URE\ r E. 657 
state tit' extreme emaciation. This latter result is difficult to explain, 
and will be discussed in another section of this vulunie. The former 
result (the hydruria) may, however, be analogous to the results of 
Bibbert'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. 
Arguments based upon the reaction of urine. — An objection which has 
been frequently urged against the nitration 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 fri >g. 
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, Dre<er 
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 
1 (ladder 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 caffehi or theobromin, or the adminis- 
tration of saline diuretics, or the production of hydraemic plethora, 
we find that the acid reaction of the nrhie 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. Biol., Munchen, 1885, Bd. xxi. S. 41. 
VOL. 1. — 42 
