56 THE HOUSE FLY DISEASE CARRIER 



were liberated in fine weather, and out of the 300 five 

 were recovered in fly traps at distances of from thirty 

 to 190 yards from the place of liberation, and all within 

 five days. He further states that he had found them 

 at an altitude of eighty feet above the ground, and 

 calls attention to the fact that such a height would fa- 

 cilitate their carriage by the wind. 



An experiment made under the direction of Prof. 

 S. A. Forbes, of which he has sent me a written ac- 

 count, indicates that house flies may spread naturally 

 for at least a quarter of a mile, going, in one significant 

 instance, from the tuberculosis hospital to the general 

 hospital of Cook County, Illinois. House flies trapped 

 at one point were sprayed with a chemical solution and 

 liberated. Then flies caught on fly paper elsewhere 

 were sprayed with another solution, the result being 

 that those which had previously been sprayed were 

 turned dark blue in color by the second solution. 



Marking Flies for Experiment 



Professor Hine found that it was a very difficult 

 matter to mark flies so that they might be recognized 

 from others, since they are very sensitive to anything 

 unusual, and any foreign substance on their bodies or 

 wings causes them to act abnormally. They contin- 

 ually try to remove the foreign substance and seem to 

 tire themselves out. He found that many specimens 

 marked with the greatest care would hardly fly after 

 they were marked, so that it was easy in many cases to 

 approach them and pick them up with the fingers. He 



