NEw York AGRICULTURAL EXPERIMENT STATION. 115 
commonly spoken of by the canners as “swells” and “ sours.” 
Cans are said to be swelled when the normally depressed ends bulge 
outward. When such cans explode or are opened the material con- 
tained is usually decomposed, vile smelling and worthless as food. 
There are at least two classes of exceptions to this description of 
the contents: Certain fruits often bulge slightly when held over 
winter in storage, but on opening they are found unchanged and 
fit for food; and cans which have undergone souring will often 
swell if kept for a time in a warm place. 
The fact that fermentations in general are so commonly caused 
by. the lower forms of plant life has led to the widespread belief 
that all the difficulties in keeping canned goods could be attributed 
to the same cause. While it is probably true that a large propor- 
tion of the swelling and souring is due to the growth of bacteria 
within the cans, undoubtedly exceptions will be found. The bac- 
teria which are capable of destroying canned goods are not only 
of different species, but what is of more importance to the canners, 
the spores of different species are capable of withstanding different 
amounts of heating. As a result of this, canners who have been 
processing successfully at a low temperature for a number of sea- 
sons suddenly find themselves in trouble when a more resistant 
species gets into the cans. | 
Swelling of peas.°—In peas, acid is lacking, the amount of 
sugar and nitrogen is such as to favor fermentation, and heat alone 
must be relied upon to prevent decomposition. In 1902 our atten- 
tion was called to a serious outbreak of swelling in the product of 
a large factory. In connection with this work we attempted to 
determine three points: (1) The cause of the trouble, (2) the 
amount of heating necessary to obviate the trouble, (3) the amount 
of heating which was allowable without injury to the commercial 
quality of the peas. 
It was found that the trouble was due to the presence of a single 
species of bacteria in the cans, and it was shown that this germ was 
able to withstand more heat than had been employed in the factory 
in canning the peas. 
Work at the laboratory showed that heating infected cans at 
240° F. for thirty minutes was sufficient to destroy this bacterium. 
The reliability of these results was demonstrated first by canning a 
ton of peas at the factory as an experiment with all the conditions 

* Bul. 249; same in Rpt. 23:47-61 (1904). 
