DAIRY INSPECTION 161 
done to keep the atmosphere as free from dust as possible. 
In other stables land plaster is spread in a thin layer on 
the floor and in the gutter to act as an absorbent. This 
is especially desirable when the floor is of wood or earth. 
The use of land plaster also seems to have the effect of 
reducing the number of flies. Although the inspector 
cannot be present during all of these operations, he can 
make a fairly accurate estimate of how thoroughly the 
work is done by observing the condition of the stable 
at the time of his visit. Dirt which has been permitted 
to remain for some time can be easily distinguished from 
fresh dirt. The wall in the rear of the cows and the 
corners formed where the walls, posts, and stall divisions 
join the floor should be especially examined. The pres- 
ence of cobwebs on the walls, ceiling, or other places is 
an evidence of infrequent sweeping. 
Flies.—The presence of flies in large numbers in and about 
a cow stable is objectionable for several reasons. The flies 
worry the cows and reduce the milk production, while the move- 
ments of the cows in their efforts to protect themselves from 
the insects interfere with milking and are also likely to dislodge 
dirt from the body of the cow; some of this dirt may fall into 
the milk pail. The common house-fly (Musca domestica) is 
especially objectionable. It feeds upon all kinds of organic 
matter, including human excrement, and becomes contaminated 
with numerous bacteria. A single fly may carry over a million 
germs on the surface of its body. When it feeds upon milk 
or crawls or falls into milk vessels, many of these bacteria are 
transferred to the milk. Typhoid bacilli may be carried from 
infected fecal matter to milk in this way. The small, black cow- 
fly or horn-fly (Hematobia serrata, Lyperosia irritans L.) and 
the stablefly or biting-fly (Stomozys calcitrans) disturb the 
cow more than the house-fly, because they are biting or blood- 
sucking insects; but they do not as a rule invade the milk 
vessels or the milk. 
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