344 PLANTS WITHOUT CHLOROPHYLL 



difficult to can, because spores of bacteria may be attached to them. 

 Fruits, on the other hand, are usually much easier to preserve. 

 After boiling for the proper time, the food, now free from all bac- 

 teria, is put into jars that have been sterilized by boiling. After 

 the boiling hot material is poured into the hot jars, they are sealed 

 to prevent the entrance of bacteria later. The cold-pack method 

 of canning consists in placing fruit or vegetables in the can cold and 

 then boiling the cans with their contents, preferably in a pres- 

 sure cooker, until all the bacteria are 

 knied. 



Uses of Canning. — Canning as an 

 industry is of immense importance to 

 man. Not only does it provide him 

 with fruits and vegetables at times 

 when he could not otherwise get them, 

 but it also reduces the cost of such 

 things. It prevents the waste of na- 

 ture's products at a time when she is 

 most lavish with them, enabhng man to 

 store them and utilize them later. 

 Canning has completely changed the 

 life of the sailor and the soldier, who 

 Pressure cooker. Steam un- jjj former times used to suffer from va- 



der pressure becomes very not 



and cooks food quickly. Tious discases caused by lack of a proper 



balance of food. 



Preservatives. — A few substances check the development of 

 bacteria and in this way preserve the food. Preservatives are of 

 two kinds, those harmless to man and those that are poisonous. 

 Of the former, salt and sugar are examples ; of the latter, formalde- 

 hyde and possibly benzoic acid. 



Sugar. — We have noted the use of sugar in canning. Small 

 amounts of sugar are readily attacked by yeasts, molds, and 

 bacteria, but a 40 or 50 per cent solution will effectually prevent 

 such growths. Preserves are fruits boiled in about their own 

 weight of sugar. Condensed milk is preserved partly by the sugar 

 added to it ; so are candied fruits. 



Salt. — Salt has been used for centuries to keep foods. Meats 

 are smoked, dried, and salted ; some are put down in strong salt 



