1889 - 90 .] Dr H. H. Ashdown on Substances in Urine . 59 
years, however, by the attempts made to define and differentiate 
the individual members of which it consists, and to ascribe to each 
their relative significance, and these efforts have been crowned in 
some measure by a considerable degree of success. 
Schmiedeberg and Mayer were the first to isolate and analyse the 
substance thus produced, and found it to be glycuronic acid, and that 
its chemical constitution was represented by the formula C 6 H 10 O 7 . 
This substance appears in the urine in combination with urea, 
from which it may be obtained by precipitation, by means of barium 
hydrate, and extraction with alcohol, and decomposition of the com- 
pound thus obtained by sulphuric acid. 
It holds the oxide of copper in solution in the presence of an 
alkali and reduces it, throwing down the suboxide, upon boiling 
ether in Trommer’s or Fehling’s tests; and a similar reaction occurs 
with the oxides of bismuth, mercury, and silver. 
For the definite recognition, however, of glycuronic acid , the only 
reliable means possessed at present is to thus obtain it pure, but, as 
already remarked, the process is long and tedious. 
The polariscope, unless used with pure solutions of this acid, or 
with solutions of known combination, is very apt to mislead, since 
some of its combinations rotate the ray of light to the left, and others 
to the right; and if glucose be also present very erroneous conclu- 
sions may be arrived at. 
When pure, it rotates the ray of polarised light to the right, — 
35°, — or to half the extent of the deflection produced by glucose. 
There is no doubt, however, that with comparatively small quan- 
tities of urine the differentiation of this substance from the glucose, 
which possesses similar chemical reactions, may be readily arrived 
at by applying the test of fermentation by yeast — a test of great 
delicacy if conducted properly and with due care over mercury, and 
one capable of demonstrating the presence of smaller quantities of 
glucose than either Fehling’s solution or Trommer’s test can detect. 
Experiments. 
I have now investigated a large number of specimens of urines 
obtained under different conditions, in order to trace as far as 
possible the presence of glycuronic acid , and to differentiate it from 
glucose. The fermentation testw r as always employed, and, whenever 
