NOTES AND MEMORANDA. 
191 
preferable is impregnation by a solution of chloride of gold — 1 in 400 
or 500. The chloride acts in preference on the points where the 
osmium is already deposited. Its action is, as is known, very incon- 
stant, and the tints which it gives very variable ; but the different 
parts of the same animalcule, coloured a uniform yellowish brown by 
the osmium, are differentiated in various tints by the action of the 
chloride. In a Philodina I found the integuments colourless, or of a 
light blue, the muscular bands rose, the intestinal tube brown, the 
cloaca black (being full), the glandular masses violet, and showing 
clearly the vacuoles and the rounded cells, with nucleus and nucleolus. 
The operative process is very simple. It is only necessary to pass 
the solution of gold under the preparation very slowly, so as not to 
carry away in the current and lose the animals which are floating. I 
place a drop of the solution on the edge of the glass and produce on 
the opposite side a very gentle suction by means of a piece of blotting- 
paper, which has been passed through the vapour of boiling water, so 
that without being wet it is not dry, and so that its suction only 
operates in proportion as it dries. I then place the preparation in 
the light and wash it (in the same way) with a current of distilled water 
until the excess of the chloride solution is removed. If the tints are 
too pronounced the preparation can be treated with a drop of very 
diluted formic acid, or mounted in glycerine. 
I have obtained less satisfactory results when the chloride is put 
upon the preparation after the osmic acid — the deposit is much more 
irregular in consequence of the presence of osmic acid in excess, 
which produces a confused precipitation of the gold.” 
A New Form of Hot Stage . — In the ‘ Bulletin de la Societe Beige 
de Microscopie ’ (vol. iv. 103) an ingenious form of hot stage is 
described by M. Benard, the invention of MM. Vogelsang and 
Geissler, and used by them in their investigations on liquids enclosed 
in the cavities of crystallized minerals. It is said to enable the 
temperature of a preparation under the microscope to be appreciated 
with great exactness, and at the same time the phases of the dilatation of 
