CHAPTER V 



ARTHROPODS AS SIMPLE CARRIERS OF DISEASE 



The fact that certain arthropods are poisonous, or may affect the 

 health of man as direct parasites has always received attention in 

 the medical literature. We come now to the more modern aspect 

 of our subject, — ^the consideration of insects and other .arthropods 

 as transmitters and disseminators of disease. 



The simplest way in which arthropods may function in this 

 capacity is as simple carriers of pathogenic organisms. It is con- 

 ceivable that any insect which has access to, and comes in contact 

 with such organisms and then passes to the food, or drink, or to the 

 body of man, may in a wholly accidental and incidental manner 

 convey infection. That this occurs is abundantly proved by the 

 work of recent years. We shall consider as typical the case against 

 the house-fly, which has attracted so much attention, both popular 

 and scientific. The excellent general treatises of Hewitt (1910), 

 Howard (191 1), and Graham-Smith (19 13), and the flood of bulletins 

 and popular literature render it unnecessary to consider the topic 

 in any great detail. 



The House-fly as a Carrier of Disease 



Up to the past decade the house-fly has usually been regarded as a 

 mere pest. Repeatedly, however, it had been suggested that it 

 might disseminate disease. We have seen that as far back as the 

 sixteenth century, Mercurialis suggested that it was the agent in the 

 spread of bubonic plague, and in 1658, Kircher reiterated this view. 

 In 187 1 , Leidy expressed the opinion that flies were probably a means 

 of communicating contagious diseases to a greater degree than was 

 generally suspected. From what he had observed regarding gangrene 

 in hospitals, he thought flies shotdd be carefully excluded from 

 wounds. In the same year, the editor of the London Lancet, referring 

 to the belief that they play a useful r61e in purifying the air said, 

 "Far from looking upon them as dipterous angels dancing attendance 

 on Hygeia, regard them rather in the light of winged sponges spread- 

 ing hither and thither to carry out the fotil behests of Contagion." 



These suggestions attracted little attention from medical men, for 

 it is only within very recent years that the charges have been sup- 

 ported by direct evidence. Before considering this evidence, it is 



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