HOW THE GREENBOTTLE DOES ITS DUTY 131 



a weakling surmount the difficulties of feeding upon the toughened 

 corpse? To answer this we must experiment in the laboratory. 

 Such a question cannot be decided by theory. We must secure the 

 eggs of the fly, hatch them under various conditions and note what we 

 can of their methods. 



For our purpose, we place several dead objects in the sunlight. In 

 a very short while there are a dozen flies about the game. Soon there 

 are a thousand ivory eggs, and in a day, as many wriggling offspring. 

 The first experiment is a huge success. We have a multitude of eggs 

 and young. Let us gather some and continue. 



In the laboratory we prepare twelve cubes of fresh raw beef, each 

 weighing three grams. Six of these are placed in separate test tubes 

 with cotton stoppers to prevent evaporation and a dozen freshly 

 deposited eggs of the fly are added to each. The six remaining cubes 

 of beef are placed under a glass bell as a control. 



In a short time the inoculated tubes are alive with young flies and 

 we notice that each individual is constantly surrounded by moisture. 

 As the youngsters increase in size from day to day, the puddle in 

 which each one feeds grows in proportion until at length after five 

 days the meat within each tube is completely liquefied and about the 

 consistency of thick cream. Under the glass bell conditions are 

 totally different. Here the meat cubes are in exactly the same form as 

 when placed there five days before. Perhaps they are slightly darker 

 in color, but they are still in the form of cubes and quite as solid as 

 ever. There is nothing which suggests a liquid state such as we see 

 in the test tubes where the young flies have been feeding. 



Continuing our experiments, we dip a piece of blue litmus paper 

 into one of the tubes of liquefied meat. It turns almost at once from 

 blue into a faded red. This is a simple chemical test which shows 

 the contents of the tube to be slightly acid. We find that the same 

 is true of the six inoculated tubes. Now in the human body there 



