INSECTS EMPLOYED IN MEDICINE, OR AS FOOD. 107 



themselves upon animal matters which, if not dis- 

 posed of in this manner, would putrefy and evolve 

 noxious gases into the air we breathe ; thus the fly 

 doubtless tends to purify the air by preventing the 

 formation of miasma. 



In this manner, Musca domestica, M. carnaria, 

 and M. Ccesar have their uses. Some flies (the 

 Blue-bottle, etc.), as I have already stated, give 

 birth to larvee already hatched ; others (M. Ccesar, 

 etc.) lay millions of eggs, whence proceed, in a day 

 or two, innumerable devourers of dead flesh. One 

 single female of M. carnaria (Blue-bottle) will give 

 birth to 200,000 young already hatched ; and Redi 

 formerly ascertained that these grubs will devour so 

 much food in twenty-four hours as to increase, in 

 this short period, two hundred times in weight. 



This will account, perhaps, for the assertion 

 made by Linneeus, that three individuals of La- 

 treille's Musca vomitaria will devour a dead horse as 

 quickly as a lion could do it. 



Many beetles devour dead flesh as eagerly as do 

 the larvae of flies. Stagnant waters are purified by 

 the larvae of the Ephemera flies, etc. 



Before quitting the subject of flies, I will mention 

 some curious results obtained lately by M. Berard, 

 who has been studying the influence of light upon 

 animal growth. His observations are applicable to 

 the whole tribe of insects. It appears from them 



