554 THE AMERICAN NATURALIST. [VOL. XXXV. 
Tue IUBE FILTER 
Numerous tests of the usual process of downward filtration 
with ordinary funnel and filter have shown that Infusoria (Para- 
moecia) can be removed from the inside of the filter only with 
the loss of a large proportion of their number, unless the filter 
be repeatedly rinsed. This results in a dilution, sometimes unde- 
sirable, and is at best an uncertain way of preventing the loss 
of organisms. To obviate these difficulties, I have employed 
another method. 
To concentrate the organisms into a small amount of water, 
to remove the culture fluid entirely if desired, and to change the 
medium at will, I have devised the following apparatus, which 
may be called a “tube filter." One end of a short piece of wide 
glass tubing is closed by a piece of filter paper held in position 
by means of a rubber band binding it to the outer circumference 
of the tube. The process depends essentially upon the quality 
and area of the filter paper employed. For rapid work with a 
quantity of about 50 cc. contained in a Stender dish I have used 
a tube approximately 3 cm. in diameter and 6 cm. in length. 
This tube is held in a vertical position by a clamp fastened upon 
aring stand. Under the tube, upon an elevated support, is placed 
the Stender dish, or preferably a deeper vessel, with the organ- 
isms. The tube is lowered until its paper diaphragm comes 
within a few millimeters of the bottom of the Stender dish. In 
the tube is hung a filled glass siphon with the lower end of its 
outer arm bent upward to prevent its running empty. As the 
water rises through the filter paper and into the tube it is 
removed by the siphon. More culture water with organisms, 
or any other fluid desired as medium, is then added to that in 
the Stender dish. The addition of the former effects concen- 
tration, as does also the final withdrawal of most of the liquid. 
This process of upward filtration leaves nearly all the organisms 
in the Stender dish when the tube is removed. By means of 4 
supplying bottle, described below, carrying an air tube and - 
siphon, water may be added to the Stender dish as fast as it 18 
withdrawn by the tube filter. This secures continuous renewal 
of the medium with practically no current. 
