Bacteriology of the Household. 725 



diately. As long as meats are kept frozen they may be preserved indefi- 

 nitely. Ordinary ice chests are very efficient for arresting the growth 

 of bacteria, although the temperature is higher and less uniform than in 

 cold storage, and they cannot Ixi depended upon for keeping foods any 

 length of time. However, bacteria grow very slowly in an ice chest. 

 The same is true in a cool cellar. 



Preservatives. — Antiseptics are materials which retard or prevent the 

 growth of bacteria. Certain materials may be used for the preserva- 

 tion of foods, which have antiseptic power ; but these should be harm- 

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

 acid, salicylic acid and formalin. In small quantities these have not 

 been found to be very injurious, but at the same time their use has been 

 made illegal in manufactured goods in many states, as their presence 

 in food might quickly lead to the consumption of amounts sufficient to 

 be harmful. . The housekeeper never knows how much pres^ervative may 

 have been used before articles of food come to her, hence it is safe for 

 her never to use them but to depend instead upon 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 the 

 latter has a detrimental influence. 



There are harmless preservatives, (a) Sugar. A heavy sugar solution 

 prevents the growth of bacteria. In the proportion of 40 to 50,1', sugar 

 makes an excellent preservative and is commonly used in this amount 

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

 raisins, figs and candied fru'ts. Condensed milk is also preserved by 

 the addition of 30 or 40/ sugar. 



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

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

 bacon, preserving eggs, hams, fish, etc. Butter and cheese are salted 

 partly for flavor but largely for the sake of making them keep better. 



(c) Acids protect food from bacteria and give a new flavor which 

 many find acceptable. In making pickles we soak cucumbers in brine 

 and add vinegar and spices to 'preserve them. The brine sometimes 

 becomes covered with a scum which is due to^ bacterial growth and the 

 pickles grow soft through decay, showing that salt by itself is not a 

 perfect preservative. The remedy is to scald the pickles in order to 

 destroy the micro-organisms. Other acids are known to preserve foods, 

 as in sauer kraut, which is protected from bacterial growth not only by 

 acetic acid but by lactic acid also, which is produced by allowing bacteria 

 to grow in the sauer kraut. The acid produced finally destroys the 

 organisms which produce it and aids in preventing the entrance of others. 



