380 



THE NATIONAL GEOGRAPHIC MAGAZINE 



The fly does far worse things than get 

 into the ointment, for unless we take 

 care he gets into or onto pretty much 

 everything we eat or drink. Such an 

 occurrence is not simply disgusting; it is 

 more or less dangerous, and the danger 

 lies in the introduction into our bodies 

 of disease germs. This danger is far 

 more real than commonly supposed. 

 There can be no doubt that much sick- 

 ness is started in this way. 



The question is. What ought we to do 

 about it? The answer is simple, and it 

 is that we ought to take greater pre- 

 cautions, both individually and collect- 

 ively — 



First. To fully inform ourselves on 

 this subject by reading and observation. 



Second. To prevent the multiplication 

 of flies. Abolish their breeding places. 

 Protect food and refuse so that flies can- 

 not get at them. 



Third. To keep flies out of our build- 

 ings and streets. 



Fourth. To employ all reasonable agen- 

 cies to destroy flies that come into exist- 

 ence in spite of our other precautions.* 



* For further information on the ravages 

 caused by flies see "Economic Loss to the Peo- 

 ple of the United States through Insects that 

 Carry Disease," by Dr L. O. Howard, August, 

 1909, Nationai, Ge;ographic Magazine, pp. 

 735-749- 



NOTES ON THE DISTANCES FLIES CAN 



TRAVEL* 



By N. a. Cobb 



IT is very difficult to make the neces- 

 sary direct observations as to the dis- 

 tances flies can travel and their rate 

 of speed — flies' motions are so rapid. 

 Nevertheless, in the course of time I 

 have been fortunate enough to witness a 

 number of convincing instances. To 

 these I have added the indirect evidence 

 of comparative anatomy. If the fly's 

 wing muscles are unusually bulky, it is a 

 fair inference that its flight will be quick, 

 or long sustained, or both. 



I have never succeeded in tiring my 

 flies very perceptibly if they had a free 

 space to move about in. When confined 

 in a room they may be kept on the wing 

 for hours without showing many signs 

 of fatigue. Though they move twenty 

 feet to the experimenter's one, they will 

 often succeed in tiring him out if he 

 undertakes the task of keeping them al- 

 ways on the wing. The instance of the 

 fly starting to cross the Mediterranean 

 Sea is a very striking one. (See page 

 382.) 



EIXPERIMENTS INDICATING THE GREAT 



POWERS OF FLIGHT POSSESSED 



BY SOME FEIES 



Among insects, as among birds, fliers 

 of two very different types are to be 

 found — those that soar and those that fly. 

 Without entering deeply into the ques- 

 tion, this division may be said to be 

 about as marked among insects as among 

 birds. The fliers among insects, to which 

 class the flies belong, correspond, how- 

 ever, more nearly to the extreme limit 

 reached in humming birds. 



The rate of wing vibration in flying 

 insects is higher than any wing rate 

 among birds. In fact, the difiference is 

 so great that it raises altogether new me- 

 chanical and physiological questions. In 

 the case of insects these questions have 

 excited the interest and attention of 

 minds of the highest order, as is appar- 

 ent on looking over the literature of the 

 question. 



The flies belong to the quick-action 

 group of flying insects, the principles of 



* Abstracted from "Fungus Maladies of the Sugar Cane," by N. A. Cobb 



