38 GENERAL SCIENCE 



the dirt and germs but will not kill them. One should 

 always wash before eating. Before performing an 'opera- 

 tion, physicians wash their hands and dip their instru- 

 ments into hot water or a solution of formalin and then 

 into boiling water. Since hydrogen peroxide liberates 

 oxygen readily, it makes a good personal disinfectant. 



(C) Chemicals as Preservatives. In the section on 

 Germs and Heat we learned that food, sealed up air- 

 tight after the bacteria, mold, and yeast had been 

 killed by boiling, would keep for a long time, the principle 

 being to keep these tiny plants out of the food after those 

 in it have been killed. In the section on Germs and 

 Chemicals we learned that these germs could be killed 

 by certain compounds as well as by the use of heat and 

 sunshine. 



These chemical compounds that will kill germs used to 

 be employed very extensively in dilute form in foods. 

 When the bacteria fell into these foods they died, and 

 hence the food would not decay or sour. This was 

 cheaper than canning. But it was a serious menace to 

 health, and no one could long endure the constant 

 use of such poisonous preservatives. So national laws 

 have been enacted prohibiting such a practice and re- 

 quiring the manufacturers to indicate on the labels the 

 quantity and kind of chemicals used, if any. These 

 laws do not prevent all the wrong use of chemical pre- 

 servatives. There are always some people who will 

 violate law, so each person should be more or less 

 on his own guard by learning the facts. 



Borax and boric acid are used on meats and will restore 

 tainted meats to the appearance of freshness. Tainted 

 meats are often made into sausage which is treated with 

 chemicals. Benzoate of soda is used in catchup. Cheap 



