A BACTERIOLOGICAL METHOD 
33 
by drawing up the fluid into the pipette several times. Approxi- 
mately 1/20 cc. of the inoculated agar is placed on a slide. Another 
slide is placed on top of it, so that about three fourths of the surface 
of the slides are in contact. This spreads the medium quite evenly 
on the two slides. They are then drawn apart and at once placed in 
a moist chamber. The agar solidifies in a very few minutes. When 
only a few slides are prepared, I have found it very convenient to 
place them in Petri dishes which are lined with wet filter paper. In so 
small a container the atmosphere becomes saturated with moisture 
in a very few minutes and later the agar film shows no indication 
of drying. If very many slides are prepared it may be found more 
convenient to use some device like the specially prepared cabinet 
described by Frost.^ 
The slides in the moist chambers are incubated until the colonies 
have grown to the desired size. The cells multiply rapidly, resulting 
in colonies of various sizes. The films are then ready to be fixed and 
stained. In the process of fixing, washing with water, staining, 
dehydrating, etc., it will be necessary to exercise great care that the 
delicate film of agar does not float off the slide. For fixing the cells 
I have used picro-formol and Flemming's weak solution diluted one 
half. The sHdes are placed in a staining jar with the fixing fluid cover- 
2L. c. 
