162 
S. Mangham. 
accelerate the formation of osazones, although by so doing the 
chances of diffusion occurring are increased. 
After cooling, the slides can be left several weeks or even 
months without harming the sections, provided air is not allowed 
to come into contact with the tissues. If it is desired to remount 
the sections they can easily be removed, washed in cold water, if 
necessary cleared by placing in 2% caustic potash for a few minutes 
and re-washing in water containing a drop or two of acetic acid, 
and then taken up by one or two stages to pure glycerine. It is 
possible to use aqueous stains to some extent, but alcoholic solutions 
cannot be employed as the osazones are soluble in alcohol. Air 
bubbles can be removed by exhausting under the receiver of an air- 
pump. Finally the preparations can be closed by applying a 
mixture of gum mastic and paraffin wax to the edges of the cover- 
slip. 1 
In order to become acquainted with the action of the reagent 
drops of solutions of pure sugars can be employed, the strengths of 
the solutions and the duration of heating being varied 
Senft himself tried such experiments with very strong solutions, 
using equal parts of water and sugar 2 . But it is preferable to work 
with much weaker solutions, such as probably exist in the plant-cell 
which is often plasmolysed by a 5% solution. 
When simply mixed with the reagent and left unheated Senft 
found that his strong solution of levulose yielded the osazone within 
a few hours, numerous sheaf-like clusters and spherical aggregates 
of needle-shaped crystals being formed. In the case of dextrose, 
however, at the end of twenty-four hours no crystals had formed, 
though the preparation shewed a lemon-yellow colour. On the 
third day a few small spherical crystal aggregates appeared. With 
both levulose and dextrose the amount of osazone produced 
increased for a few days. Cane sugar was found to give no osazone 
crystals in the cold even at the end of five days. 
In other experiments drops of the strong solutions were heated 
with the reagent for periods varying from five minutes to half-an- 
hour and the changes produced were observed on removing the 
slides from the water-bath. Levulose, after five minutes, exhibited 
an orange-yellow colouration the depth of which increased as the 
heating was prolonged. At the end of half-an-hour the slide was 
1 For a description of this convenient method of closing glycerine 
preparations, cf. Thomas, H. H., New Phytologist, March, 
1911, pp. 105, 106. 
2 L.c., p. 10. 
