HOW HOUSEFLY AND MOSQUITO AFFECT HEALTH 429 



furnishings, if it is to make any real headway against dust 

 and the disease germs which the dust contains. 



Light and air are nature's agents for the destruction of 

 germs "in the open"; we need these in our houses also 

 (cf. 246). One of the worst results of dust and dirt in 

 the house is that they cover up the germs, and prevent 

 light and air from getting at them. As we call the in- 

 vasion of our bodies, our homes, or our clothing, by harm- 

 ful germs, infection, so we call the 

 destruction of such germs disinfection. 

 The agents, or materials, that cause 

 germ destruction we call disinfectants. 

 The most common disinfectants of the 

 household' are soap and hot water. 

 There are also chemical disinfectants 

 that are very useful for special pur- 

 poses (cf. 438). Disinfection by gases 

 is called fumigation. 



424. How the Housefly and Mosquito 

 Affect Public Health. There is little or 

 no use in arguing the question whether 

 or not the fly does anything for man; 

 we have abundant evidence of what he M g . 303. 



does to man. Flies grow, as maggots, in Foot of i a ^S fly> ^ 

 the body waste of animals; they feed in 

 all manner of dirty places; they enter sickrooms, and come 

 away loaded with disease germs (Fig. 303). Not only do 

 germs cling to the fly, but they are present in the dis- 

 charges of its body (' ' fly specks ") . This evidence against 

 the fly is enough to exclude it from our tables, our dishes, 



