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- 

 tice when new, but not infrequently 

 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 

 loo^ C. 



Tubes should always be steamed 

 in wire-crates (fig. 44) so that the 

 streaming steam ma}' have full access 

 to all parts. Tubes of media steamed 

 in cans or beakers often spoil. They 

 seem to retain a cushion of air about 

 them which interferes with the action 

 of the steam. 



Litmus milk. — Litmus milk of a 

 good equality may be made by dissolv- 

 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. Li 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. 



Loeffler^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, i. t'., 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 difiicnlt. 

 The albumen of eggs may be cut with sterile scissors. 



Fig. 44.- 



*FiG. 44. — Wire-crate for liolding tulied culturc-nicdia wliicli is to be stcaniefl. About two- 

 fifths actual size. y\ tuft of cotton on tlie bottom prevents tlie breaking of tubes. 



