DISINFECTANTS AND DISINFECTION 351 



preservation. Chemical preservatives make it possible for the unscrupu- 

 lous to use decomposed and otherwise objectionable food material. Fur- 

 thermore, there is a strong tendency to use chemical preservatives in 

 excess, in spite of the strictest legal quantitative limitations. 



The following is a brief summary of the more common food preserva- 

 tives and their use. 



The physical and mechanical means of food preservation have been 

 referred to, likewise the use of heat, cold, smoke, etc. One of the most 

 satisfactory methods of preserving foods, now employed in all up to date 

 canneries, is a combination of heat sterilization with air exclusion (air 

 pump and by displacement). The food products as meat, corn, beans, 

 asparagus, peas, jams, jellies, preserves, etc., etc., are heated (100 C. to 

 120 C.) to destroy all germ life, the containers (tins, glass) are also heated 

 and then nearly filled to exclude as much air (oxygen) as possible. Air 

 (oxygen) is necessary for the growth of bacteria, yeasts and molds, hence 

 a well filled container, with a minimum of oxygen is less likely to show 

 decomposition effects ("swells," " leaks") than containers which are not 

 well filled. It is claimed that wholesome fruit, meat, etc., (free from 

 decomposition), which is well sterilized by steam heat and put up in well 

 sterilized containers requires no chemical preservative whatever. It is, 

 however, customary, in the case of fruits, to add sugar as a preservative 

 and also for the purpose of rendering the article more palatable. The 

 sugar from sugar cane is quite universally used in preference to the sugar 

 from the sugar beet. This is no doubt due to the fact that sugar beet 

 sugar contains slightly more organic impurities and is, hence, under 

 similar methods of use as to quantity, degree of heat sterilization, etc., 

 slightly more likely to undergo decomposition. 



Preservation of food substances by drying is coming into use more and 

 more. By this method it is possible to keep, for variable periods of time, a 

 great variety of foods as apples, peaches, pears, bananas, potatoes and 

 many other vegetables, besides bread, meats, eggs, milk and other sub- 

 stances, which were formerly more generally preserved by the canning 

 method. Eggs may also be preserved entire by giving them a coating of 

 tallow, wax, paraffin or soluble silicate, which exclude the air, or they may 

 be preserved in brine, salt or other so-called harmless chemical preservative. 



Herring, cod and other fish are often preserved in a brine of salt or of 

 equal parts of salt and borax or boric acid. Of meats, fish is particularly 

 liable to decomposition and it is declared that certain kinds cannot be 

 preserved in salt alone, that it is necessary to add boric acid, rubbing the 

 preservative well into incisions made along the spinal column where the 

 decomposition develops earliest. Salt is used with meats generally and with 

 butter. Two per cent, of salt in butter is sufficient, though as much as 



