62 
AGAR-AGAR. 
Ill the preparation of this, medium beef broth prepared as already 
described was used in every instance. For the most part, peptone did 
not seem to be required in the preliminary studies, and no time was 
spent in using it to determine additional differences in the growth ot 
the microbes studied. The agar-agar was finely cut before being placed 
in the broth to soak. It was found that the difficulty as to cloudiness 
in the media could be greatly lessened by soaking the agar-agar in 
water for a time and thoroughly washing before placing it in the broth. 
With these preliminary explanations, the following may be given as 
the formula, which is also the one used by Prof. Forbes and Prof. Bur- 
rill: 
One quart beef broth. 
Ten grams agar-agar. 
Five grams sugar (yellow clarified). 
Five grams salt (druggist's best). 
After shaking well, allow to staud and soak over night. 
The following morning boil for three, hours. Strain until clear; cool 
to about 60° C. Stir in the white of an egg and boil until well coagu- 
lated. Strain until clear; neutralize if necessary; keep hot without 
boiling, and allow to stand for fifteen minutes. Filter; sterilize for an 
hour. If sediment forms, filter again; sterilize for another hour, and 
let stand over night. If upon warming the next morning a sediment 
forms, filter again, after which it will be safe to fill the test tubes. These 
are then further sterilized the same as beef broth. After the last ster- 
ilization of the tubes the wire cage containing them should be laid on 
an inclined plane, so as to give a slanting and therefore greater surface 
in the tube for the growth of the germs. 
The agar agar medium sometimes looks slightly cloudy while yet hot 
or upon being heated, but, as in the broth, this disappears upon cool- 
ing. 
SPECIAL APPARATUS. 
The filtering of agar-agar and other solid media is often attended 
with great difficulties in winter, since the hot liquid cools and thickens 
so rapidly. For this reason an apparatus for hot filtering is necessary. 
A separate appliance requiring additional gas and burners is in com- 
mon use. Your agent was compelled to secure the necessary apparatus 
speedily and economically, and accordingly the following combination 
of the steam sterilizer and hot filter was devised (see Plate n, Figs. 
A, B, C, D, E). The lower portion (A) of the sterilizer was made as 
usual; this particular one 10 inches in diameter and 1 foot high, with 
three circles of tips («, «, a) on the inside, on which to lodge the 
perforated diaphragms (B) at various heights above the water. The 
legs (b) were high enough to allow an ordinary two-burner oil stove to 
