26 
OF THE FREE DIATOMACEiE. 
Fig. 37. 
rapidly, forming a brown layer on the surface of the mud. 
As soon as a sufficient quantity is produced, the water is 
carefully poured away, or (preferably in my opinion) is 
drawn off by the aid of a small 
glass syringe. The mass is now 
to be swept up with a camel’s 
hair pencil, and either deposited 
at once on a slip of glass, or im- 
mersed in clear water. The mud 
remaining in the plate may be a 
second time moistened and placed 
in the sun, and the collection of 
the Diatomacese repeated as be- 
fore. By degrees, however, the 
vitality of the little plants ex- 
hausts itself, and it is necessary 
to revive their vegetative powers. 
This may be accomplished by 
creating for them an artificial 
spring and winter. And there is, 
in truth, no difficulty in pro- 
ducing these unseasonable sea- 
sons ! You have only to allow 
the water to evaporate, and the 
mud to become nearly, not quite, 
dry. Then pour fresh water 
over it, and once more the Dia- 
tomacese break up, and vegeta- 
tion commences anew. In this 
way, gatherings originally poor 
may be made to yield an abun- 
dant supply of plants. 
Another contrivance for obtaining the Diatomacese in a 
pure state is the washing apparatus of Benning, fig. 37. 
It consists of a glass cylinder, two feet six inches in 
height and two inches wide, on one side of which four 
holes are pierced, c, d , <?, f the lowest at four inches from 
f 
