176 



BACTERIA, YEASTS, AND MOLDS 



tightly plugged with cotton, as shown in Fig. 64, it will 

 be perfectly protected from the invasion of bacteria. A 

 knowledge of this fact may be of some practi- 

 cal importance, even in the household, in case 

 it is desired to preserve something for a short 

 time only and one does not want to go to the 

 trouble of hermetical sealing. But such a 

 method is quite impracticable for the ordi- 

 nary canning of food. At best it is of only 

 temporary utility, for, though cotton keeps 

 all bacteria away from the sterilized material, 

 it will not wholly exclude molds, and there- 

 fore cannot preserve indefinitely. 



Hermetical sealing, which will prevent all 

 subsequent access of air, is extremely easy to 

 accomplish and is thoroughly effective. The 

 material must be sealed in some proper re- 

 ceptacle while still hot from the boiling, for 

 it is at this time sterile, and if sealed at once 

 has no opportunity of becoming inoculated 

 with more bacteria. 



The devices for hermetical sealing are 

 served cher- numerous. In earlier days the housewife 

 ries, showing ^^^ joy^d ordinary bottles, which were filled 



that the ex- ^ ^ / .... 



elusion of air with the material, then plugged tightly with 

 is not neces- corks, and sealed with rosin or something of 

 saryforpres- ^|^g g^j-j. ^^ exclude all air. The invention 



ervation. . , , - . . • , . , , 



of the modern frutt jar with its rubber nng 

 and convenient top has done away with all such crude 

 devices. The fruit jar with its variously devised top is 

 a perfectly effectual means for excluding air and hence 



Fig. 64. Pre- 



