DISINFECTANTS 41 



for application to cattle trucks, the walls and stalls 

 of cowsheds, stables, dairy premises, and other farm 

 buildings, which are liable to become infected with 

 germs of disease, or with bacteria which pollute milk 

 and do damage to dairy products generally. 



Soda or sodium carbonate (Na 2 CO 3 ) is also useful 

 for the cleansing of domestic utensils of all kinds, its 

 alkaline character having a similar action upon micro- 

 organisms to that of lime. 



For the preservation of foods of all kinds from decay 

 and putrefactive changes, the use of poisonous substances, 

 such as mercuric chloride, carbolic acid, and formaldehyde 

 is, of course, prohibited. Much, however, can be done 

 by drying, smoking, heating, and the addition to the 

 food of harmless materials, such as sugar, salt, and 

 saltpetre. 



Fruits of many kinds, which often contain 80 to 90 

 per cent, of water, may be preserved by drying them, 

 the low water-content of the dried product being in- 

 sufficient to allow of the free growth of bacteria, especially 

 when sugar is present, the latter acting in some degree 

 as an antiseptic agent. 



In the case of jam, the addition of sugar is combined 

 with boiling of the material, and a similar practice is 

 adopted in the preparation of condensed milk, 10 or 12 

 per cent of sugar being added to the milk, the water- 

 content of which has been reduced by evaporation to 2 5 

 per cent, or less. 



In the " canning " or " tinning " industry, which deals 

 with vast quantities of fish, vegetables, and other perish- 

 able foods, reliance is placed upon the destruction of 

 bacteria contained in them by means of heat. The 

 sterilization of the tins and their contents was formerly 



