22 BULLETIN OF THE BUSSEY INSTITUTION. 
appear after a time when the precipitate and supernatant liquor 
have been left to stand for a few days. In such mixed pre- 
cipitates characteristic crystals of mannose-hydrazone and of 
dextrose-osazone may be seen under the microscope lying side by 
side. Even on recrystallizing the mixed crystals from warm 
diluted aleohol, both kinds may reappear unless the recrystalliza- 
tion is carefully conducted. In his book* entitled ‘* Physiology 
of the Carbohydrates,” Pavy has published a number of micro- 
photographs of osazone crystals as obtained from the hydrolysis 
of albumin and of a variety of other animal matters, — notably, 
muscular tissue, liver, spleen, and kidney, and of osazone crystals 
from blood and urine also. Many of these figures are exact 
representations of crystals obtained in this laboratory in number- 
less instances from the dextrose present in the products of the 
hydrolysis of the cellulose in woods of various kinds that were in 
process of being tested for mannan. 
« To avoid as much as may be possible the formation of dextrose- 
osazone, the mixture of the phenylhydrazin reagent and the solu- 
tion under examination should neither be heated nor left to stand 
too long in the air. After allowing a reasonable time — about 
two hours — for the formation of the mannose-hydrazone precipi- 
tate, it is well to pour off the supernatant liquid and to remove 
the excess of the reagent by washing the precipitate with cold 
water. Since dextrose-osazone is soluble in glacial acetic acid, 
mannose-hydrazone may be freed from it either by drenching 
the ‘‘ original precipitate” with this acid before examining the 
precipitate under the microscope, or, in case of need, a drop of 
the acid may be allowed to flow in upon the precipitate under 
the cover-glass on the slide of the microscope. This use of the 
glacial acid is of special importance in the case, which may happen 
not infrequently, where the spines on fringed or roughened 
globules of mannose-hydrazone are so small that the eye cannot 
determine whether they have sharp points, like needles, or blunt 
and bevelled ends. On mere inspection of such ‘‘ sea-urchins,” 
doubts would arise as to whether they were mannose-hydrazone 
or dextrose-osazone, though a recrystallization from alcohol will 
* F. W. Pavy, Physiology of Carbohydrates, London, 1894. A German 
translation of this book, made by K. Grube, was published in ners and 
Vienna in 1895. 
