ZOOLOGY AND BOTANY* MICROSCOPY* ETC. 
311 
I is opened, and when the acid reaches the same level in both parts 
of the gas generator, quickly close M, and then close I just as soon as the 
change of level in the generator shows that there is a slight excess of 
pressure in A. After sealing, the tube is transferred to the ice block 
and rolled until the agar or gelatin is solidified. In case of agar, the 
rolling must be very rapid to ensure good results. The apparatus is 
also of service for displacing the air from other forms of anaerobic cul- 
ture apparatus. If the vacuum pump used is capable of giving a column 
of mercury 635 millimetres high in the tube D, five-sixths of the gases 
in the tube A will be removed at each exhaustion. A simple calcula- 
tion will satisfy the operator in regard to the number of exhaustions 
necessary. 
Preparation of Culture Media and their Sterilisation.* — Mr. R. 
C. Reed recommends the following methods for the preparation of 
nutrient media. 
Pejotonised Bouillon . — To 1000 grm. of finely divided meat, add 
2000 grm. of distilled water, and place in an agate or iron dish, and then 
heat in a water-bath at from 60°— 65° C. for two hours, or allow it to 
macerate in a cool place for 24 hours. Strain through a coarse cloth, 
and bring the amount of liquid up to 2000 ccm., adding water if 
necessary. Then add 0*5 per cent, pepton, and 0*5 per cent, sodium 
chloride ; and, if a neutral or alkaline medium be desired, add enough 
of a 1 per cent, solution of caustic soda. Boil in a water-bath for half 
an hour. Cool, and filter through ordinary filter paper, and distribute 
in sterilised flasks. 
Nutrient Agar . — Dissolve 5 grm. of finely cut agar in 100 ccm. of 
water, and then add it to 500 ccm. of bouillon and boil for 20 minutes. 
Cool down to 45°-50° C., and add the whites of two eggs. Return to 
the water-bath and boil for 20 or 30 minutes. In this way the clot 
will be got rid of, and a perfectly clear liquid left. Filter through 
ordinary filter paper wdiile hot, and distribute into sterilised tubes. 
Nutrient Gelatin . — To 500 ccm. of bouillon add 50 grm. of gelatin, 
and heat in a water-bath until the gelatin is dissolved. Cool to about 
45° C., and then add the whites of two eggs, mixing the lot thoroughly. 
Boil in a water-bath for about 20 minutes. Filter, and distribute in 
sterilised tubes. Care must be taken not to boil the gelatin too long, 
lest it will not set when cold. 
The author goes on to point out that lengthy discontinuous sterilisa- 
tion may be overdone ; for he has found that sterilising for one day 
for 30 minutes usually suffices. All that is necessary is to incubate 
afterwards for several days, and then reject the few tubes which are 
contaminated. 
Rapid and Easy Method for Preparing Nutrient Agar.f — Herr 
E. S. London prepares agar in 33 minutes in the following way : — To 
1 litre of meat water are added 5 grm. of salt, 10 grm. of pepton, and 
15 grm. of agar, and the mixture placed in a flask which is heated in 
an autoclave until the temperature rises to 130°. The steam is then 
gradually slacked off, and when the temperature has sunk to 100° the 
* Amer. Monthly Micr. Journ., xviii. (1897) pp. 149-54. 
f Centralbl. Bakt. u. Bar., l te Abt., xxi. (1897) pp. 686-7 
2 A 
1897 
