1266 



The Cornell Reading-Courses 



spores begin changing over to the active, growing, vegetative type of 



organism and in their greater " Hveliness " they lose much of their power 



to resist heat and cold and other unfavorable 



influence. 



If spores had found their way to some food that 



was to be preserved by canning, the amount of 



heat applied in the old way of canning foods 



might not have been sufficient to destroy them. 



Then, after the jars containing the food were 



sealed and set away, ample food and moisture and 



possible warmth being supplied, the spores changed 



over to the active growing form and, as a result, 



the food began to work, mold, 



_ or decay, according to the kind 



Fig. 8o. — Spring-top jar r 



or organism present. 



If a reasonable time of cooking serves to destroy 



micro-organisms only in the vegetative form and 



leaves spores alive, then food canned by such cooking 



is always in danger of spoiling. If, after sealing, 



all conditions of growth are favorable, the spores 



present begin to change over to the vegetative 



form. Twenty-four hours will accomplish the 



change from spore to vegetative form. If the food 



is cooked again, however, micro-organisms in the 



vegetative form will be destroyed. A few spores. Fig. 8i.— Position of 



more resistant than all the spring during sterili- 



zatton 

 Others, may still linger. There- 

 fore, it is wise to make assurance doubly sure by 

 letting the food stand twenty-four hours longer, in 

 order to permit the development of the remaining 

 spores into the vegetative form, afterward cooking 

 the food a third time. The best methods for 

 obtaining good results are described on page 267 

 of this lesson. 



The commercial canner has solved the problem of 

 sterilization in another way. A temperature higher 

 than the boiling point of water is more destructi\'« 

 Fig. 82.— Position of than is that of boiHng water, and when the tem- 

 ^prmg after sieriliz- ^^^^^^^^ ^g high enough a relatively short time of 



cooking is sufficient to sterilize all foods subjected 

 to such a temperature. As a result, canning factories are equipped with 

 mechanical devices for cooking foods at high temperatures. By careful 



