THE HOUSE-FLY 



THE ADULT FLY 



The adult fly is about one-fourth of an inch in length 

 and has two thin membranous wings, the fifth longitudinal 

 veins of which turn abruptly upward near the ends (Fig. 

 1). The dorsal side of the thorax is dusty gray in 

 color and has four dark, longitudinal 

 stripes. The legs and the body are 

 covered with many hairs and bristles, 

 among which great quantities of germs 

 are easily entangled and carried from 

 place to place. Moreover, each one of 

 the six feet is furnished with two 

 sticky pads called pulvilli (Fig. 4). 

 Each pad, or pulvillus, is thickly beset 

 with tiny hairs, which secrete minute 

 drops of a sticky liquid that literally 

 sticks the fly to the ceiling upon which 

 it is walking. Unfortunately, these 

 sticky hairs, in addition to enabling 

 the fly to walk upside down, form 

 ideal organs for picking up all sorts of FIG. 4. Foot of 

 bacteria from the filthy materials upon 

 which the fly walks. Thus we see the 

 house-fly is fitted in many ways for gathering and carry- 

 ing germs. In fact, it cannot help but gather bacteria 

 from the various things upon which it alights and then 

 distribute them far and wide, for it wipes its feet upon 

 everything it touches. The relation of the fly to the 

 germs that it carries is purely a mechanical one. It has 

 been shown repeatedly that house-flies do carry multi- 

 tudes of bacteria. In Fig. 5 is shown a plate of gelatine 



house-fly, showing 

 pulvilli, enlarged. 



