New York AGRICULTURAL EXPERIMENT STATION. 51 
such material in many cases is an admission of either carelessness 
or ignorance on the part of the canner. 
It is a matter of common observation that the absence of a 
vacuum means trouble. From this has grown the idea that the 
vacuum itself prevents decomposition. Nothing could be farther 
from the facts. The souring of peas often progresses to a point 
where the peas are worthless before the vacuum is destroyea. 
Moreover, cans of peas will keep satisfactorily in free contiect 
with the air if, before processing, the opening is provided with 
a cotton plug so as to prevent germs from entering. 
The vacuum is useful in decreasing the tension in the can in 
connection with the heating and its absence indicates a leak 
which will allow germs to enter. 
Commercial canning depends very largely upon heat as a 
means of preventing undesirable changes; and the progress of 
the business has been marked by improvements in the means of 
heating and in the knowledge of the effects of various degrees 
of heat. Beginning with open tanks of water which were lim- 
ited to 212° F. there has been developed the closed kettle where 
all temperatures up to 250° F. are in use. Prescott and Under- 
wood stated? that when working at 236° F. that temperature was 
found at the center of a 2 lb. can of standard packed peas in 10 
minutes while it took 40 minutes heating at 250° F. to raise 
the center of a like can of corn to 236° F. 
BACTERIA AND THEIR ACTION. 
For convenience members of the plant world are often referred 
to by groups. The members of one of these groups, characterized 
by their small size and simple form are referred to as bacteria. 
Like mould spores and yeast cells the individual bacterium (plural 
bacteria) is too small to be seen by the unaided eye but like 
both mould and yeast it often grows into a mass which can be 
readily seen. 
Food can be used by plants only when it is in solution, so that 
the germs live, not on the vegetables directly, but upon the sol- 
uble material in the cans. . By means of enzymes which they 
secrete they are able to soften the solid vegetables. They all 
2Paper before Rochester meeting of Canners’s Association. Trade 23: 
No. 29, Feb. 22, 1901; alsojCanner and Dried Fruit Packer of same date, 
