DISINFECTION 229 



escape through the dough, so it simply forms in bub- 

 bles, making the mass " light." In baking, the alcohol is 

 mostly driven out and the heat stops any further action 

 of the yeast. 



269. Disinfection. The bacteria of which we have 

 studied are very numerous ; there are also many differ- 

 ent kinds. They are too small to be seen without a 

 strong microscope, except in masses composed of many. 

 Some kinds of bacteria are harmless and some are even 

 useful, but a few kinds are known to be the cause of 

 certain diseases in animals and man. These kinds are 

 usually given off in some quantity from persons who are 

 ill with such diseases ; and as they may be taken into 

 the bodies of other persons and there cause illness, it is 

 important to try to kill the "germs." 



The killing of these bacteria is called disinfection. 

 Many methods are used. Heat is of great use, as a tem- 

 perature of 100 C (boiling water) will destroy all com- 

 mon forms in a short time. All dishes and cloths used 

 by the patient should be carefully boiled in water, and 

 papers should be burned. Fresh air in the sick room is 

 important, and sunlight kills many bacteria. For a liquid 

 disinfectant, weak solutions of carbolic acid or of some 

 chlorides are good, but nothing seems to equal a weak 

 solution of corrosive sublimate in water (1 part in 1000). 

 After all, the best way to avoid diseases is to keep 

 ourselves clean and keep our general health at the 

 highest. Many disease germs doubtless enter the body 

 of a well person and do no harm because of his strong, 

 healthy condition. 



