LABORATORY WORK 335 
filter through the cotton to be caught below in a beaker or flask. It should be 
transparent, clear, and of a yellowish-brown color. If it is not clear a second boiling 
with a second egg will usually clear it. 
Fic. 58.—Showing method of hardening agar slants. 
Place 10 c.c. of this agar medium into each of 25 test-tubes and plug with cotton. 
In filling these tubes use either a 10 c.c. pipette or a funnel, taking care not to allow 
the agar to touch the sides of the tubes where the cotton is to be inserted. 
(e) Place the test-tubes, together with the flask containing the remainder of the 
Fic. 59.—A steam sterilizer (Fowler). 
medium (tightly plugged with cotton) in the autoclave and sterilize at 15 pounds for 
30 minutes. Cool,-and after the pressure is down to zero, remove from the autoclave. 
While still hot lay the test-tubes down on a table with their mouths slightly raised, 
so that the agar will form a slanting surface (Fig. 58). Allow them to harden in this 
