132 INSECT BEHAVIOR 



exists a ferment in the gastric juice known as pepsin, which in the 

 presence of a weak acid converts proteids or tissue-forming foods into 

 peptones, that they may be easily diffused through the membranes and 

 used in the actual building and heating of the body. The strip of 

 litmus has shown us the presence of just such an acid in each tube of 

 liquefied meat. 



Here then is the solution of the mystery surrounding the young 

 flies' method of feeding. They are born without an equipment, suit- 

 able for actually chewing, but Nature has supplied them with a 

 powerful expectorant capable of dissolving flesh into bouillon. Like 

 so many drunkards, they drink their dinners, but their intoxication 

 which comes only in the form of life, rids us of decay, a menace to 

 our health and welfare. 



From a chemical point of view, the young greenbottles digest their 

 food in much the same manner that we do, but being unable to chew 

 and swallow solids, they exude their pepsin first upon the food, con- 

 verting it into liquid, which is then easily drawn into their suckling 

 mouths and swallowed. Indeed it is a most admirable method, one 

 that we would not be loath to mimic were our jaws undeveloped, our 

 mouths toothless and our limbs unsprouted. So much for the young 

 flies' method of assimilating their food. 



Let us make the final experiments so that we may realize how this 

 insect is of service to mankind. There are fifty thousand species of 

 flies and we cannot condemn them all like the filthy house fly and the 

 fever mosquitoes, which are recognized outlaws of humanity. In the 

 ranks of this huge winged army we find insects doing good as well as 

 bad, and the greenbottle is one of them. 



For our experiment we procure a banana, two kinds of fungi, 

 some granulated sugar, the boiled white and yolk of an egg, some 

 gluten and a bit of cheese. It is a weird collection to be sure, but it 

 will serve our purpose very well. We have now eight different food 



