310 LABORATORY WORK. 



correct. It should require 1.5 c.c. of i/io normal NaOH to neutralize 

 the acidity in 10 c.c. If the reaction is right, cool to about 60 F. and add 

 the white of an egg which has been mixed with a little water, adding slowly 

 with stirring. Heat slowly and allow to simmer until the egg has co- 

 agulated and the liquid is clear. This may take half an hour or more. 

 Add water to bring to the original weight again, plus the weight of the 

 added egg, and then filter as follows: 



d. Place a considerable quantity of absorbent cotton in a large funnel 

 (Fig. 58). Over the top of a second funnel above the first, place some cheese- 

 cloth. Pour the hot agar medium into the cheese-cloth. It will run through 



FIG. 58. Showing method of filtering culture media. 



rapidly ; then 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. 



Place 10 c.c. of this agar medium into each of 25 test-tubes, replacing 

 the cotton plug. 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 remain- 

 der of the medium (tightly plugged with cotton) in the autoclave and steril- 

 ize at i 5 Ibs. 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 



