ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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method gives a whiter wool without brittle and partly charred thread, 
and by it tubes can be prepared in one day. When about half a gross 
of tubes have been plugged they are replaced in the hot-air sterilizer 
and raised to 150° for an hour. 
To prepare sterile nutrient gelatin, one pound of lean beef is 
finely minced, and a litre of tap water is poured over the mass ; the 
whole is placed in the steam sterilizer for an hour and a half, and is 
then filtered into a large beaker containing 100 grm. of gelatin, 
10 grm. of peptone, and 5 grm. of salt. The hot filtrate quickly 
dissolves the gelatin. The mixture is now placed in the steam steri- 
lizer for half an hour, neutralized with potassium carbonate, or replaced 
in the sterilizer for another hour. The turbid fluid is now filtered 
into a large flask and distributed to the sterile plugged tubes ; these 
are now steamed for fifteen minutes, and the steaming is repeated on 
the second and third day for ten minutes each day. This treatment 
is quite effective. 
Before opening the tubes the tuft of wool was uniformly singed to 
burn up the dust and germs which might have fallen on the outside. 
In the preparation of sterile peptone broth the only difference is that 
the 100 grm. of gelatin are omitted. For sterile agar-agar 20 grm. 
of agar are used instead of 100 grm. of gelatin. Petri’s dishes 
(shallow covered glass dishes about a decimetre in diameter and 15 mm. 
deep) are much more simple to work with and give less contamination 
from the air than the original glass plate and bell-jar method. 
Investigation of Chemical Bacteriology of Sewage.* — Sir H. E. 
Roscoe and Mr. J. Lunt adopted the following method for the isolation 
of anaerobic organisms. They devised a special form of cultivation 
flask (fig. 66) suitable not only for mixed cultures, but also for pure 
cultures, in which the organisms can be grown in an atmosphere of pure 
hydrogen. 
The flask is furnished with a capillary tube e, sealed in at /, for the 
purpose of introducing hydrogen. A firm plug of sterile wool at g 
excludes foreign germs. When it is desired to sterilize the flask and its 
contents before the introduction of pure material or sewage, the fine jet 
a is sealed, and the opening c, for the introduction of the culture fluid 
and organisms, is protected by a sterile plug d. The whole is steamed 
for twenty minutes on two or three successive days, and is then ready 
for use. The plug d is carefully removed, and a few drops of sewage 
are introduced by a freshly drawn out capillary pipette, after which the 
tube is sealed at c. Pure hydrogen is now passed through the liquid by 
means of the capillary tube e, the gas issuing by the broken off end of 
tube a, immersed in water to shut off all communication with the air. 
After the gas has passed for half an hour and every trace of oxygen is 
expelled, the flask is hermetically sealed at h and b. 
For the isolation of spore-forming organisms the following method 
was used ; a few drops of sewage were introduced into a sterile broth 
tube by means of a recently drawn out capillary pipette, and the plug 
was replaced. The tube was then plunged into water at 80° for 
ten minutes ; this suffices to kill all the full-grown bacilli, but is not 
* Phil. Trans., 182 B (1892) pp. 635-7, 
