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 (1911), and Graham-Smith (1913), 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 1871, 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 should be carefully excluded from 
wounds. In the same year, the editor of the London Lancet, referring 
to the belief that they play a useful role in purifying the air said, 
“Far from looking upon therh 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 foul 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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