SANITARY PRIVY. 15 
number of hours, and, besides that, the ground under and around the 
outhouse becomes polluted. 
Even if such a privy is provided in the back with a tightly fit- 
ting trapdoor, so as to exclude domesticated animals and to prevent 
the toilet paper from being blown about, its efficiency is increased by 
only about 15 points, so that it should not be ranked more than 25 on 
a scale of 100. Insects, such as flies, ants, and roaches, still have 
access to the night soil, which also pollutes the ground under and 
around the privy. 
The kinds of privies that are sanitary.—A sanitary privy must meet 
the following requirements: 
(1) The excreta must not touch the ground; hence some kind of 
water-tight receptacle (box, pail, tub, barrel, tank, or vault) for the 
excreta must be used under the seat. 
(2) Domesticated animals must not have access to the night soil; 
therefore the privy should have a trapdoor in the back to exclude 
them. 
(3) Flies and other insects must not have access to the excreta; 
therefore the entire privy must be made rigidly flyproof, or some 
substance must be used in the receptacle to protect the contents from 
insects. 
Two types of sanitary privies are generally recognized, namely, 
the so-called “ dry system” and the so-called ‘“ wet system.” 
THE “ DRY SYSTEM.” 
In the “ dry-system ” privies dry earth, road dust, wood ashes, or 
lime is kept in the privy, and is scattered on the excreta every time 
the privy is used. 
The dry system, if properly managed, presents the following 
advantages: 
(1) It decreases the offensiveness of the privy contents. 
(2) It is cheap. 
(3) It decreases the chance of spread of infection by insects. 
(4) It is an easy system to manage. 
The disadvantages of the dry system are the following: 
(1) It is very difficult to make a dry privy rigidly fly proof, hence 
flies usually do have more or less access to the excreta, on which 
they feed and on which they lay their eggs. 
(2) Its efficiency depends upon the careful and faithful coopera- 
tion of all persons (including children) who use the privy, and 
experience shows that such cooperation can not be relied upon. 
(3) It increases the amount of material to be removed; hence it 
increases the labor and frequency of necessary cleaning. 
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