2/8 The American Naturalist. [April, 
the middle one having- a width of 4-5 cm., the two others 2 
cm. only. It is on these three slips that are placed the object 
slides bearing- the infusoria. The whole is covered by a glass 
plate, fitted as hermetically as possible to the edge of the 
dish. The dish being filled with rain water up to the hori- 
zontal strips, the air space is reduced to a layer of 4 or 5 mm. 
in thickness. This layer of air is always saturated with moist- 
ure, and the preparations suffer only an extremely feeble 
evaporation. 
For sorting and transporting infusoria, glass pipettes, about 
10 cm. long, are used. The tapering end should be thin, and 
its opening not over i mm. in diameter. The infusoria are 
first placed en masse in a large dropof water upon a slide, and 
examined with a low magnifying power. The inside of the 
pipette is wet by filling it once with water. An infusorian 
having been selected under the microscope, the mouth of the 
pipette is placed near that side of the drop of water where the 
infusorian is found. As soon as the pipette touches the drop, 
a portion of it is drawn in by capillary attraction, carrying 
with it the specimen sought, together with, perhaps, others 
not wanted. The contents of the pipette are expelled upon 
a second slide. If the drop contain several infusoria, a drop 
of rain water is added, and the manoeuvre with the pipette 
repeated. In this way the isolation of an infusorian may be 
surely and rapidly accomplished. After each operation with 
the pipette, it should be washed with care, by forcing fresh 
water through it several times. Some infusoria have a strong 
adhesive power, and it often happens that they are left ad- 
hering to the internal surface of the tube ; hence the impor- 
tance of washing after each experiment. 
The isolated individual is covered with an ordinary cover- 
slip, preferably one 18 mm. square. The cover-slip may be 
supported by small pieces of bristles from a tooth-brush. As 
these pieces have a mean thickness of about .3 mm., it follows 
that the space inclosed represents a volume of about 100 cu. 
mm., and will hold 10 eg. of water,- or about 5 drops. The 
entire space should be filled with water. It is very important 
in such work to use pipettes, slides, and slips that are perfect- 
ly clean. The least trace of a reagent left on the cover-slip 
may be enough to render the whole preparation valueless. 
Infusoria thus inclosed and protected may live indefinately 
under perfectly healthful conditions. Supplied with proper 
food, they will develop and multiply with all the energy of 
their highest power of reproduction. 
Supply of food. In order to supply carnivorous species 
easily with food, it is necessary to find among the more com- 
