322 AGRICULTURAL BACTERIOLOGY. 



the readiness with which a food product yields to the canning 

 process is largely dependent upon the question whether it is 

 likely to contain resisting spores. Practical experience has 

 shown that some foods are much more easily canned than 

 others. Tomatoes have always proved difficult to preserve in 

 this way, and the housewife has probably more trouble with 

 this product than with any other. For a long time it was 

 thought to be impossible to preserve green corn by canning, 

 for, in spite of careful methods, most of the cans were found 

 to undergo some kind of fermentation. The canning factories 

 have mastered both of these products, but even in the best fac- 

 tories there is a considerable loss of the product by subsequent 

 fermentations. In these cases it has been demonstrated, by 

 careful bacteriological study, that the trouble is exactly what 

 theoretically we would anticipate. In the spoiled cans are 

 bacteria with very resistant spores which have withstood the 

 heating of the first step in the process. It is interesting to find 

 that the same bacteria which occur in the spoiled cans of corn 

 are found upon the corn and its husk while still growing in the 

 field (Fig. 37). The reason for the difficulty of canning corn is 



FIG. 37. 



' 



V 



O o 



Three species of bacteria causing the spoiling of canned corn. (Present 7 and I 'nder-n'omi.') 



thus apparent. The corn, while growing in the field, is infested 

 with a certain species of bacteria which produces resisting 



