DIFFICULTIES OF CANNING 173 



impossibility to can green corn, and the preservation of peas 

 and beans has proved to be even more difficult. While 

 all of these products are successfully preserved by canning 

 to-day, it is chiefly done in factories ; for they are far more 

 difficult to preserve in this way than a large number of 

 other foods which are more commonly preserved in the 

 home. The problem of canning any product, whether it 

 be fruit, tomatoes, corn, or peas, is simply that of totally 

 destroying the bacteria that may be 

 present. If the material chances to 

 contain only the bacteria that are 

 unable to produce spores, as with 

 most fruits, it is quite easy to 

 destroy them by simple boiling. 

 Green corn, however, has been *V 

 found by microscopic study to con- FIG. 63. Spore-producing 

 tain a considerable number of a cer- bacteria found in canned 

 tain kind of bacteria which develop 



spores capable of resisting very high heat (Fig. 63). These 

 bacteria have been found on the corn husks while grow- 

 ing in the field, on the corn cobs, and also in the green 

 corn. They are difficult to destroy by heat, and hence 

 the successful canning of corn has been regarded in 

 past years as an impossibility. The presence of two or 

 three or even one of these highly resisting spores may 

 be quite sufficient to make the ordinary method of can- 

 ning quite ineffectual. Although little microscopic study 

 has been directed to other similar problems, like the can- 

 ning of tomatoes and peas, there is no doubt that the 

 trouble is due to the presence of spore-bearing bacteria 

 which resist the temperature of ordinary boiling. 



