558 THE AMERICAN NATURALIST. [VoL. XXXV. 
USE oF ABSORBENT COTTON IN MAKING MICROSCOPIC 
PREPARATIONS. 
Temporary or permanent preparations, permitting the fre- 
quent change of fluids under the cover-glass that is often 
required in micro-chemical work, can be made successfully by 
means of absorbent cotton. This method is very well adapted 
to the preparation of entire Infusoria. With the forcepsa very 
small quantity of.dry absorbent cotton, free from thick masses, 
is placed in position upon a well-cleaned slide. With a pipette 
a drop or two of water containing the Infusoria is placed upon 
the cotton. No more water should be used than can be 
absorbed by the cotton, which is then spread apart with two 
needles until the desired thinness of distribution of the fibres 
is reached. The cotton should occupy about the area of the 
cover-glass to be used. Both quantity and distribution must 
be learned by experience. A cover-glass is then lowered hori- 
zontally upon the preparation. If a hanging drop is to be 
transferred to the slide, the cotton is distributed while dry and 
the cover-glass lowered in the same manner. Two rubber 
bands, of such size as to exert some but not much pressure, 
are then passed around the cover-glass, one at each end. 
Fluids as desired are now passed under the cover-glass by 
adding them in drops at its upper end when the slide is placed 
in a more or léss slanting position. The fluids emerging from 
the lower end of the cover-glass are permitted to run down the 
slide freely, or are guided down by means of a strip of filter 
paper. When the latter device is used, and with the larger 
Infusoria, the rubber bands may be removed after the passage 
of the fixing fluid, and all subsequent fluids slowly added in 
drops and entirely removed with filter paper, the: slide in this 
case being kept in a horizontal position. In most cases the 
whole slide, held vertically and with rubber bands in position, 
may be alternately dipped into and raised out of the fluids to 
be applied ; but balsam had better be added in drops, as above 
described. 
Finally the rubber bands are removed. The cotton ened 
used is a sufficient mechanical obstruction to prevent the 
