202 INSECTS 



tions, and afterward over plates of prepared gelatin. 

 In the incubator, every footprint developed a flourish- 

 ing colony of virulent cholera germs. 



The mouth parts of flies are almost equally well 

 adapted for similar purposes. At the end of the fleshy 

 lips are lobe-like expansions furnished with chitinous 

 ridges by means of which the pasty masses of food are 

 scraped into shape to be ingested by the insect. These 



FIG. 93. Lapping organ at the tip of the fly mouth. 



ridges are excellent resting places for the minute organ- 

 isms and, when the flies change their diet, the germs are 

 directly inoculated into the new food material, what- 

 ever its character. And flies are not always cleanly in 

 their habits, but void their excrement anywhere in 

 small, pasty masses which dry quickly. It has been 

 shown that the bacilli of intestinal troubles pass through 

 the digestive tract of the insect unchanged, hence every 

 "fly speck" may be a source of danger. 



This method of transfer for pathogenic organisms is 

 very simple and direct, and is applicable only to forms 



