48 BACTERIA IN RELATION TO PLANT DISEASES. 
bottom the water drips to the lower bottom and is quickly converted into steam 
which streams through a central chimney into the bottom of the sterilizing chamber. 
The latter has two walls, with a considerable air-space between, open at the bottom. 
The streaming steam passes over the top of the inner wall downward into this air- 
space and escapes into the pan as condensation water. ‘Theoretically this is a very. 
perfect sterilizer, and it is so in prac- 
at tice when new, but not infrequently 
1 <1 it leaks, and sometimes the openings 
in the upper bottom are too large or 
become clogged by mud. When in 
perfect working order it takes only a 
few minutes to get.a temperature of 
100° C. 
i ‘Tubes should always be steamed 
in wire-crates (fig. 44) so that the 
i streaming steam may have full access 
= : toall parts. Tubes of media steamed 
bs in cans or beakers often spoil. They 
x. + seem to retain a cushion of air about 
; Lt pL them which interferes with the action 
AZ Tee of the steam. 
tects Litmus ‘milk.—Litmus milk of a 
JIB good quality may be made by dissoly- 
ing Merck’s dry, lime-free c. p. blue 
litmus to saturation in distilled water 
(1:15) and then adding one part of this blue fluid to each fifty parts of milk. The 
milk should be a deep lavender color. Much inferior litmus is on the market. 
Large use should be made of this fluid. In addition to observations under “ Milk,” 
note how rapidly the litmus reddens, blues, or becomes reduced, and how soon the 
color returns. Will it return at once on steaming the culture? 
Rice cooked in milk.—(One or two grams to 10 cc, in each test-tube). This is 
useful for study of some chromogens. 
Loeffier’s solidified blood-serum.—Observations under this and the following 
heads are the same as for gelatin slant cultures. The plant bacteriologist must in 
general obtain blood-serum from the animal bacteriologist. The solidified serum 
may also be used plain, z. e., without the addition of grape-sugar. 
Egg-albumen,—This is solidified and used in the same way as blood-serum. 
The end of the egg from which the albumen is poured must be thoroughly flamed 
before it is broken,.and «care must be used in the transfer to test-tubes so as to 
exclude air-borne germs as far as possible, otherwise the sterilization will be difficult. 
The albumen of eggs may be cut with sterile scissors. 
Fig. 44.* 
*Fic. 44.—Wire-crate for holding tubed culture-media which is to be steamed. About two- 
fifths actual size. A tuft of cotton on the bottom prevents the breaking of tubes. 
