2 INSECTS AFFECTING HEALTH OF MAN OR ANIMALS, 
HOW THE HOUSE FLY CARRIES DISEASE. 
The habits of the house fly render it dangerous to the health o 
man, especially in temporary or semipermanent arrangements of © 
camp life where there is a large amount of excreta and refuse with — 
only primitive or makeshift methods of disposal. House flies not — 
only breed in and feed on these accumulations of excrement and 
refuse, but, as everyone knows, they also frequent kitchens and — 
mess tents. They will pass from excrement to food and vice versa. — 
The great importance of this insect in connection with military — 
operations was clearly shown during the Spanish-American War. : 
A special board of medical officers, consisting of Reed, Vaughan, ~ 
and Shakespeare, investigated the pace and made a most note- 
worthy report, from which the following is quoted: 
We are satisfied that the evidence furnished in our studies, to be detailed later, is 
sufficient to show beyond reasonable doubt that the most active agents in the spread 
of typhoid fever in many of the encampments in 1898 were flies. The reasons for 
coming to this conclusion will be given in detail later, but may be summed up here as 
follows: 
(1) The latrines contained fecal matter specifically infected with typhoid bacillus. 
(2) Flies alternately visited and fed upon this infected fecal matter and the food | 
in the mess tents. More than once it happened, when lime had been scattered over 
the fecal matter in the pits, that flies with their feet covered with lime were seen | 
walking over the food. 4 
(3) Typhoid fever was much less frequent among members of messes who had their _ 
tents screened than it was among those who took no such precaution. 4d 
(4) Typhoid fever gradually died out in the fall of 1898 in the encampments at — 
Knoxville and Meade with the disappearance of the fly, and this occurred at a time 
of the year when in civil practice typhoid fever is generally on the increase. 
HABITS OF THE HOUSE FLY.! 
The eggs are laid in horse manure, human excrement, pig manure, — 
and to a less extent in other manure, in decaying grain, moist bran, ~ 
moist mixtures of hay and grain from feed troughs of animals; in 
excreta-soiled straw, paunch contents from slaughtered animals, 
decaying kitchen refuse, and rotting fruits and vegetables; in excreta- 
soiled paper and rags, and in ensilage. | 
Hach female fly may lay as many as 120 eggs at one time, and as — 
a rule several flies will deposit in the same spot, so that the eggs are 
usually found in clusters or nests, in cracks and crevices of the © 
manure or other material. The size and appearance are well illus- ~ 
trated in figure 1. | 
The moisture and heat of the fermenting substance in which the © 
eggs are laid cause them to develop rapidly, and within 10 to 24 © 
hours the maggots hatch out. These maggots feedin the manure or | 
other material, keeping below the surface. If conditions are favor- 
able, they reach full size within 4 days. Figure 2 shows them at 
this stage. When full grown and fully fed, they migrate from their 
1 Musca domestica L. 
