178 BACTERIA, YEASTS, AND MOLDS 



This greatly restricts the number of materials that can be 

 used for food preservation. Some it is quite impossible 

 to use because of their violently poisonous nature. For 

 example, carbolic acid and corrosive sublimate will prevent 

 decay perfectly, since they are fatal to bacterial growth; 

 but they are also violent poisons to man and hence must 

 not be put in his foods. There are other chemicals, how- 

 ever, of a less poisonous nature which are frequently used 

 for the preservation of foods. 



The milder drugs in use to-day for this purpose are 

 chiefly borax, benzoic acid, salicylic acid, and formalin. 

 Although these substances are poisonous and injurious 

 to man when used in considerable quantity, they may be 

 swallowed in small quantities without any appreciable 

 effect upon the individual. But even in small quantities 

 they have the power of checking the growth of bacteria, 

 and they are frequently used for protecting various kinds 

 of food from the spoiling that would otherwise occur. 



These materials, put up into proper form for use, can 

 be found in our markets under a variety of commercial 

 names. These various commercial products differ in their 

 chemical analyses, but are all made up of mildly poisonous 

 materials. No two of these .preservatives are exactly alike, 

 but most of them are made up, wholly or in part, of the 

 chemical substances above mentioned. At one time a num- 

 ber of such products were sold quite generally, under special 

 trade names ; but to-day one rarely finds them offered for 

 sale by retailers in the United States. They are now known 

 to be of questionable value. They are undoubtedly effi- 

 cient in protecting food from putrefaction and decay, for 

 they all check bacterial growth. If used in sufficient quan- 



