THE HOUSE-FLY AS A CARRIER OF POISON GERMS. 36 9 



experiment that flies were capable of conveying such spores to plants and other 

 bodies. On the other hand, the fact that by far the greater part of the spores 

 were consumed, in the one case by the larvae of the fly and in the other (/'. e., 

 when mixed with sugar,) by the fly itself, shows that this insect may destroy 

 microscopic germs as well as disseminate them, and indicates that in some cases 

 its agency in keeping down their number may more than counterbalance its ac- 

 tion in contributing to. their dissemination. 



In another experiment a quantity of yeast was mixed in water and placed 

 under a glass receiver into which the fly-trap had previously been emptied. The 

 flies partook sparingly of the yeast fungus, and after the lapse of forty-eight hours 

 several of them were found dead, but the rest, amounting to several hundreds, 

 appeared wholly unaffected. On examining the abdomens of the dead flies I 

 found them congested and cheesy; and when the intestinal contents were mixed 

 with pure water, a drop placed under the microscope was found to be strongly 

 charged with both spherical and rod-bacteria and with several kinds of spores, 

 but very few spores of the yeast-plant were seen. Several flies, which were im- 

 mersed for a moment in yeast water, died in about twelve hours after immersion, 

 while those not so treated sustained no apparent injury, though confined several 

 days in the same chamber. But I do not consider the experiment conclusive as 

 to the injurious effects of the external application of yeast on flies. J propose to 

 test this question more fully at a future time. 



The odors of the yeast on the fourth and fifth days, although very obnoxious 

 to the human olfactories, did not seem to affect the health of the fljes. In my 

 next experiment, several hundred flies were confined in a glass receiver as before, 

 in which was placed about an ounce of fresh beef thinly cut. A small quantity 

 of pure water was also suppHed in a watch-glass. The flies for a while enjoyed 

 the beef and the water. Their consumption of the beef was proved by well defined 

 cavities which they made in it, and the fact that solid tissue was thus consumed 

 by the flies affords another evidence of the facility with which the eggs of augui- 

 lulae, including those of trichinae, if present in meat partaken of by them, might 

 be passed through their proboscis along with food. 



On the fifth day of their confinement I observed that a number of the flies 

 died within the chamber. By this time the meat was in a state of advanced de- 

 composition, and its odors were very offensive. 



In comparing the results of this experiment with those of the one last de- 

 scribed, it appears that the odors emitted from decomposing beef were much 

 more hurtful to the flies than those proceeding from decomposing yeast. I re- 

 moved with a knife all the soft surface portions of the beef which were exposed to 

 the flies my object being in part to ascertain whether any auguilulas had been de- 

 posited on the beef by the flies. I also examined the water for auguilulse, but failed 

 to find any in either case. On two occasions I have observed an auguilula bore 

 through the membrane of the anterior portion of the proboscis of the fly and 

 emerge from the hole thus made. In using a power of about 500 diameters un- 

 der favorable conditions it will be seen that these animals are armed with a bor- 



