372 



THE NATIONAL GEOGRAPHIC MAGAZINE 



tragic circumstances. No mosquitoes, no 

 malaria. No mosquitoes, no yellow fever. 



In sanitary matters the tragedy that 

 appeals to us strongly enough to make 

 us do something worth while must be a 

 tragedy quick in its action and very 

 awful in its results. One is almost 

 tempted to say that if only a disease is 

 insiduous enough it may proceed without 

 opposition, even though we know all 

 about its cause and the means for its 

 prevention. How otherwise can we ex- 

 plain the prevalence of consumption? 

 One hundred yellow-fever victims per 

 week move us more than the regular 

 mortality from consumption that same 

 week, though the latter may be a hun- 

 dred times the greater. 



If consumption laid hold of its victims 

 suddenly and took them off in a few 

 days, what a difference it would make 

 in our attitude toward it ! And yet it 

 does far worse. It lingers and tortures 

 its victim, often for years, making life 

 a burden to him and to his friends, a 

 continual source of care and expense, a 

 continual source of sorrow, and, worst 

 of all, a continual menace to all who 

 come in contact with him or his belong- 

 ings. It does worse, while we too often 

 continue to tread the old beaten track, 

 more or less apathetic, failing to do what 

 we know we ought to do. 



However interesting and horrible this 

 psychological aspect of consumption may 

 be, I wish at the present time to do no 

 more than make it illustrate the attitude 

 we have assumed toward flies, which is 

 hardly less interesting and deplorable. 



But people are beginning to ask, if the 

 mosquito is so important a factor in 

 human diseases, whether the people who 

 for a generation or more have been call- 

 ing attention to the house-fly as a dis- 

 tributor of disease may not have a case 

 worthy of attention. The result has been 

 a slow and partial awakening, so that we 

 now have municipalities with sufficient 

 enlightenment and courage to begin the 

 fight against flies. I say courage very 

 advisedly, because it takes courage of an 

 uncommon sort, in matters of this kind, 

 to act up to convictions we know are not 

 shared by the majority of our neighbors. 



Fighting public indifference is a thank- 

 less task, especially when it is accom- 

 panied by an undercurrent of half -con- 

 scious guilt. 



We have been slow to recognize the 

 important part insects play in the spread 

 of disease, because it is difficult to catch 

 them in the act. The insects themselves 

 are small and elusive, and the disease 

 germs even more so. It is a rare occur- 

 rence for us to know at what time, or 

 precisely in what manner, we have be- 

 come infected with the germs of disease. 

 It is almost always a matter of guess- 

 work. If, therefore, any one is skeptical 

 about the dangerousness of flies, and 

 asks to be shown a case in which it can 

 be proved that flies have infected a 

 human being, he sets a difficult task. 

 There is no difficulty whatever in caus- 

 ing flies to come into contact with viru- 

 lent germs, nor is there any difficulty in 

 showing that they can transfer these 

 germs to healthy animals, and that the 

 animals in consequence become diseased. 

 This has been done and constitutes one 

 of the main proofs of the dangerousness 

 of flies. 



There is plenty of evidence that flies, 

 having come into contact with diseased 

 material, have afterwards by their con- 

 tact with persons or their food probably 

 caused the disease that followed. This, 

 however, does not constitute that rigid 

 and satisfactory proof we would prefer. 

 Nevertheless, such histories can now be 

 assembled in numbers that amount to the 

 strongest kind of circumstantial evidence. 

 There are a number of diseases whose 

 annual increase and decrease harmonize 

 with the abundance of flies in precisely 

 the way they would do if flies were the 

 inoculating agency. The circumstances 

 fully warrant us in accusing the fly of 

 transferring almost any infectious dis- 

 ease that occurs in fly-time. 



The fly's power to spread disease is a 

 direct function of its powers of locomo- 

 tion. It can fly considerable distances at 

 a high rate of speed. It is quickly car- 

 ried long distances by trains, boats, 

 teams, animals, and man. 



It is possible to get a good idea of a 

 fly's rate of flight in a number of ways. 



