No. 415.] THE STUDY OF INFUSORIA. 555 
THE U-CELL For RENEWABLE MEDIA. 
Another device, which I shall call the U-cell, serves much the 
same purpose as the tube filter, but on a smaller scale. It has 
the advantage of facilitating microscopic observation and of 
permitting more rapid change of medium. 
To make this U-cell (Fig. 1) there are necessary two slides 
(best thin), a few rubber bands, and darning cotton of large 
diameter and close fibre. A piece one and a half times the 
length of the slides used is held at one end 
with the forceps and dipped into water until 
thoroughly wet, care being taken not to loosen 
its fibres or to make its diameter uneven by 
rough handling, although after dipping it may 
be drawn lightly between thumb and fingers to 
insure complete wetting. This is then laid 
lengthwise upon one slide (which is best placed 
across the top of an open Stender dish) in the 
form of a long U, and the other slide laid upon 
it. The ends of the U barely project beyond 
the parallel ends of the slides at the open end 
of the cell. 
Two or three rubber bands — doubled so as 
to exert more pressure, if the smaller Infuso- 
tia are to be kept in it; otherwise not —are passed around 
the slides crosswise. This arrangement constitutes the U-cell. 
The darning cotton used should be of such a size as will 
cause the slides to be about O.5 mm. apart when the rubber 
bands have been applied. This dimension and also the 
length of the U should be so regulated as to admit of the 
convenient use of a capillary pipette for the withdrawal of 
organisms. A shorter U should be obtained by the use 
of shorter slides, not by altering the proportions given above. 
Under the magnifier any selected individuals can be taken 
Cut. To fill the cell, water containing Protozoa is injected 
With a small pipette into the open end of the U, while the cell 
Stands nearly vertical. A portion of the water will flow out 
through the cotton yarn, but capillary attraction will keep 
Fic. 1. 
