THE HOUSE-FLY 



379 



my possession gained through the use of 

 a little counter which can be used to 

 estimate the number of fly specks on a 

 given area. 



We men-folks are much less observant 

 in this matter than our better halves, but 

 even a man, after a short period of train- 

 ing, finds no difficulty in astonishing him- 

 self at the abundance of fly specks in 

 situations that show them off to advan- 

 tage ; for instance, on ordinary window 

 panes. No housewife needs to be told 

 that one of the main reasons for cleaning 

 windows is the presence of fly dirt, but 

 even she will, I think, be surprised at the 

 results of actual counts. The fact is we 

 ordinarily notice only the largest and the 

 darkest. The great majority escape no- 

 tice because they are small or transparent 

 and colorless. Window panes with from 

 I, GOO to 10,000 fly specks per square foot 

 are not at all uncommon. From 10 to 

 50 per square foot is a common number 

 in what are considered well-kept homes. 

 Spotless glass is rare, except on house- 

 cleaning day. 



This is in situations where the dirt 

 can be readily seen. On neutral tinted 

 objects, less often cleaned, fly specks 

 occur in millions. On wall-paper, chan- 

 deliers, outside veranda posts, on cor- 

 nices, ceilings, and window blinds the 

 numbers are almost past computation. 



The amount of this fjecal matter de- 

 posited by flies is of course in proportion 

 to the number of flies. When the flies 

 have access to diseased or rotten or fotfl 

 matter these faeces are dangerous. If 

 there is any infectious or contagious dis- 

 ease in your neighborhood in fly-time, 

 beware of flies ! 



Flies swallow the germs of typhoid in 

 countless millions while feeding on the 

 excreta of typhoid patients. As a result 

 they spread a thousand times more ty- 

 phoid germs in their excreta than on 

 their feet. My own experiments have 

 shown that the spores of a variety of dis- 

 eases pass through various species of flies 

 without appreciable change, and that 

 without doubt certain diseases produce 

 odors that entice flies to swallow the 

 spores so that these latter may be more 



efficiently spread abroad. The germs are 

 just as virulent after passing through the 

 fly as before. 



My experiments show that the greatest 

 variety of spores and microbes can, and 

 normally do, pass through flies and ger- 

 minate afterwards. In fact, the most deli- 

 cate spores are litde if any injured by 

 the fly's digestion. Among those tried 

 are the spores of some of our commonest 

 and most destructive moulds and spores 

 of nearly all the diseases of sugar-cane 

 and those of numerous other plants. In 

 short, it rarely happens that spores of 

 any kind swallowed by a well-fed fly do 

 not appear in an hour or so in the faeces 

 of the fly in an uninjured condition, such 

 that they germinate readily afterward. 

 Finally, as might be expected, examina- 

 tion of the excretus of flies captured in 

 the open shows it to contain a great 

 variety of spores in a living condition. 



I find the digestion of the adult fly 

 to consist in the absorption of those sub- 

 stances readily soluble in its weak digest- 

 ive fluids and the evacuation of all others. 

 In accordance with this principle the fly 

 is an enormous feeder. At a single meal 

 it frequently swallows nearly half its own 

 weight of food. In the course of a day 

 a well-fed fly probably as a rule swallows 

 more than its own weight of food. 



During the summer the fly population 

 of any large town must number millions. 

 Comparing this fact with the food habits 

 of the fly, we see at once the importance 

 of the role they play in our afl^airs, more 

 particularly in view of their disease- 

 carrving powers. I venture to think the 

 most powerful imagination fails to take 

 in the vast multitude of conclusions that 

 follow from these simple lines of rea- 

 soning. 



What has been said is an attempt to 

 show that the house-fly is a character of 

 much greater significance to us than is 

 indicated by his adornment of a fable. 

 He really does have something to do with 

 the turning of the wheel, but it is the 

 wheel of life. He mav have little to do 

 with keepino- it going, but he certainly 

 sometimes has much to do with stop- 

 ping it. 



