780 THE AMERICAN NATURALIST. (VoL. XXXIX. 
with enough water to cover. It is best to get material from 
several localities. If Ceratophyllum cannot be found, Elodea 
and various other plants may be used, but the results are less 
satisfactory. 
Bring the material to the laboratory and there set up cultures 
as follows. Use “bacteria dishes" — shallow circular glass 
dishes, about 9 inches in diameter and 3 inches deep. Pack 
the material in these firmy, crushing it down. This will pre- 
vent growth of the plant, and favor fermentation. Pack to 
within an inch of the top of the dish, and add just enough 
water to cover the material. Cover the dishes with glass 
plates and put them in various warm and well lighted places 
about the laboratory. Each culture should be labeled with the 
place where the material was obtained, and the date when the 
culture was set up. Later, as organisms appear which are to be 
. Studied, their »ames should be added to the labels. Zabel the 
dishes, not the covers. If water evaporates so as to expose the 
plant material, enough should be added from time to time to 
make good the loss. 
The first cultures should be started about tree weeks before 
the Amoebz are needed. A half dozen cultures should be 
Started at this time and several new ones added every two or 
three days thereafter, until the class is nearly through studying 
Ameeba. The time required for the cultures to mature varies ; 
a single culture may last but a few days, and not all are success- 
ful — hence the necessity for frequent collections and many 
cultures. j 
The first indication of Amceba is a brown or a white scum 
appearing on the surface of the water. This consists mainly 
of bacteria, and the Amoebz come to the surface to feed on 
them. Take up a bit of the scum with forceps, mount in a 
drop of water taken from the surface with a pipette, tease out 
the scum thoroughly with needles, and examine with a micro- 
Scope. Amæbæ, if present, will usually be found among or near 
the particles of scum. Also, remove a bit of the plant mate- 
rial and scrape the slime from it. This will often contain more 
Amoebe than the scum at the surface of the water. The speci- 
méns are small at first, but in a few days they become larger. 
