512 FOOD PRESERVATION 
a little after the can is cooled. Bitting points out that incubation at 
37° C. and at from 50 to 55° C. for fifteen days should precede the bac- 
terial examination. 
The second step, is the opening of the can, which must be carried 
out under very carefully controlled conditions. The can should be 
thoroughly sterilized about the place for opening either by flaming or 
covering with alcohol and allowing it to burn off. The can may be 
opened by cutting around the top with a sterile can opener or a hole 
put through the top by a sterile awl. The contents for examination 
may then be removed by means of a sterile loop or a sterile pipette. 
When the hole is punched into the can a flame should be played on the 
spot so that no bacteria will be sucked into the can with the air. The 
can should be entirely opened, later as soon as possible, in order to deter- 
mine the appearance of the contents. 
The third step, is concerned with the actual microscopical examina- 
tion. This should be direct as well as cultural. The direct methods 
of examination have been sufficiently discussed elsewhere in this book. 
The cultural methods require special media such as corn, agar, tomato 
bouillon, etc., depending upon the substances which are being exam- 
ined. Such media create for the organisms which are searched for, an 
environment as much as possible like the normal. Both aerobic and 
anaerobic methods of culture should be used. It is often advisable to 
incubate the cultures in a vacuum, to come more nearly to the conditions 
inside of the can. 
Organisms in Canned Foods. These have not received very extended 
study. Much of our knowledge must come from analogy and there 
is some danger in reasoning thus. In relatively few instances has time 
been taken to identify the various varieties of microorganisms. Bur- 
gess (1912) isolated and identified about 12 organisms from “ flat sour ” 
corn. Among others, he found B. coli, B. acidi lacticit, Ps. syncyanea, 
B. megatherium and B. vulgatus. The first work on the bacteriology of 
canned foods in this country was done by Russell (1895). He exam- 
ined swelled canned peas. He isolated two organisms, one of which 
was & copious gas producer. Prescott (and Underwood, 1897, 1898, 
1900), gave this subject quite a little attention. They did much to 
establish the close relationship of bacteria to the spoilage of canned 
foods. The importance of the canned food industry should stimulate 
the examination of these foods. 
The author has found spore-forming facultative anaerobes to be 
common. In a few cases vegetative cells have been isolated. In one 
case mushrooms packed in brine of the following composition—5 Ibs. 
