HOUSEHOLD BACTERIOLOGY 61 



that drying only arrests the growth of bacteria, and that when food has 

 over 30 per cent of moisture there is danger of its spoiling. Dried 

 foods are therefore kept in a dry place so as to prevent absorption of 

 moisture and consequent spoiling. 



Cold-storage 



As a means of preventing putrefaction and decay, storehouses are 

 cooled artificially and a low and constant temperature is maintained. 

 Eggs, fruit, vegetables, and the like may be kept for a considerable period 

 of time if they are frozen, and may then be delivered at the market in fair 

 condition for use. There is some question, however, regarding the safety 

 of the use of cold-storage foods, for food deteriorates quickly if it is taken 

 from cold-storage and not used immediately thereafter. As long as meats 

 are kept frozen they may be preserved indefinitely. Ordinary ice-chests 

 are very efficient for arresting the growth of bacteria, although the tem- 

 perature in them is higher and less uniform than in cold-storage and they 

 cannot be depended on for keeping foods for any length of time. Bac- 

 teria grow very slowly, however, in an ice-chest. The same statement 

 is true regarding certain materials that have antiseptic power in a cool 

 cellar. 



Preservatives 



Antiseptics are materials that retard or prevent the growth of bacteria. 

 They may be used for the preservation of foods, but they should be harm- 

 less to man. Substances often used as preservatives are borax, boracic 

 acid, salicylic acid, and formalin. In small quantities these preservatives 

 have not been found to be very injurious; yet their use in manufactured 

 foods has been made illegal in many States, as their presence in food 

 might quickly lead to the consumption of amounts sufficient to be harm- 

 ful. The housekeeper never knows how much preservative may have 

 been used before articles of food come to her, hence it is safe for her never 

 to use any preservative but to depend instead on the bactericidal action 

 of heat. It is not known how much the digestive organs can endure 

 from borax and similar materials, but experiments seem to show that such 

 materials have a detrimental influence. 



Harmless preservatives. (a) Sugar. A heavy sugar solution prevents 

 the growth of bacteria. In the proportion of 40 or 50 per cent, sugar 

 makes an excellent preservative and is commonly used in this amount in 

 the preparation of jellies, marmalades, and preserves and in preserving 

 raisins, figs, and candied fruits. Condensed milk is also preserved by 

 the addition of 30 or 40 per cent of sugar. 



(b) Salt is very commonly used in the household to prevent bacterial 

 growth. The housekeeper uses it for keeping fat pork, for corning beef and 



