26 BULLETIN OF THE BUSSEY INSTITUTION. 
reagent to solutions of mannose, will often be seen to increase 
from hour to hour, or even from day to day, when the mixture is 
left to stand, it is still true in ordinary testing that the hydrazone 
balls and crystals appear much sooner than the osazone crystals, 
which would naturally be deposited later than the mannose-hydra- 
zone, since they are not present in the solution at first but are 
formed there subsequently and somewhat slowly by way of oxida- 
tion. Hence, it happens that the speedy appearance, in any 
given case, even of imperfect or doubtful globules or crystals on 
the addition of the phenylhydrazin reagent, is of the nature of 
presumptive evidence that some mannose is present, and the 
experimenter should be encouraged to continue his search for it. 
Conversely, the total absence of balls or crystals until many hours 
after the application of the test would indicate that there is little 
chance of finding any mannose in that solution. 
In comparison with the above mentioned trials with pure dex- 
trose, others were made with commercial ‘‘ glucose” and with 
‘¢ starch sugar.” To one portion of a dilute solution of glucose 
there was added eight drops of the mixture of phenylhydrazin 
hydrochlorate and sodium acetate, and the mixture was heated 
on a boiling water-bath for an hour. ‘The precipitate contained, 
beside the amorphous dust, many clusters of small, round globules 
that were opaque and thick, and it did not change in appearance 
in the course of three days. To another portion of the glucose 
solution sixteen drops of the phenylhydrazin reagent were added, 
the mixture was heated for an hour as before, and a similar pre- 
cipitate was obtained that did not change in appearance on standing 
for two days. ‘To yet another portion of the glucose solution 
twenty drops of the reagent were added and the mixture was 
heated as before. After several hours a few carpet-like patches 
of small, round, reddish globules were detected, but the appear- 
ance of the precipitate did not change in two days. 
For the sake of comparison, the ordinary clinical test * for 
* As is well known, the formation of dextrose-osazone is an essential 
feature of a highly approved method of detecting sugar in diabetic urine. 
Descriptions of this test as employed by different chemists vary as to details, 
and some of the methods give better results than others. The method here 
described has given me excellent results. In the hands of Pavy, the ready 
formation and detection of osazones had led, to a masterly exposition of the 
facility with which hexoses may be obtained by the hydrolysis of albuminoids 
and proteids. 
