76 PRACTICAL ZOOLOGY 



How GERMS ARE CARRIED. The house fly is important 

 because it carries on its body or in its alimentary canal many of 

 the pathogenic bacteria. Flies very easily become soiled with 

 particles of filth in which millions of bacteria live, and this filth 

 is transferred to any object upon which they alight. Most of the 

 germs are carried upon the legs, or are taken into the alimentary 

 canal and vomited or deposited as excreta. That the legs are 

 very easily soiled is due to the presence upon them of numerous 

 hairs among which the germs become lodged (Fig. 49). Hairs 



FIG. 50. The lapping organ at the tip of the proboscis of the house fly. 



(After Smith.) 



on other parts of the body may likewise catch groups of bacteria. 

 The number of bacteria on a single fly has been found to average 

 about 1,250,000. 



The mouth parts of the house fly also aid in the distribution of 

 germs. They are modified for lapping and form a sort of pro- 

 boscis. This is a fleshy organ about as long as the head, with 

 two lobes at the top covered with very fine ridges (Fig. 50). 

 Within the proboscis .is a tube leading to the stomach. Solid 

 food, such as sugar, must be liquefied before it can be swallowed. 

 The fly does this by pouring out upon it a little saliva and then 



