CONVICT LABOR FOR ROAD WORK. 107 
they need not be uncovered except for cleaning and filling. Wooden 
covers are not satisfactory, as they do not fit tightly enough to keep 
out mosquitoes and are liable to warp. Cesspools and privies must be 
constructed in such manner as to prevent access of mosquitoes, while 
tin cans, broken bottles, sagging gutters, holes in rocks, hollows in 
trees, or any other places which may hold water and serve as breeding 
places for mosquitoes, should not be allowed to remain about a camp. 
Areas of stagnant water, when they can not be drained, should be 
treated once every ten days with a half and half mixture of crude oil 
and kerosene. 
Screens and mosquito bars are indispensable in keeping out mos- 
quitoes wherever they are prevalent, and in some places both screens 
and bars will be found necessary. At those camps in which steel con- 
vict cages are in use screening is comparatively simple and inexpen- 
sive, and satisfactory results are obtained by carefully screening the 
four open sides. Experience has shown that mosquitoes can some- 
times pass through a metal-wire screen containing 16 strands or 15 
meshes to the inch, but can not pass through one which contains 20 
strands or 19 meshes to the inch. 1 Screens made of iron wire are 
cheapest at first cost, but require painting in order to make them last 
through a season. The paint reduces the size of the mesh, so that 
ventilation is interfered with to a considerable extent. On the other 
hand, screens of brass or copper last almost indefinitely and though 
expensive at first may be cheapest in the end. 
Mosquito bars are well adapted for camp use and should be a part 
of the regular equipment in regions where mosquitoes are numerous. 
They may be suspended from the ceiling and tucked in around bunks 
or may be arranged so as to rest upon the floor all around the bed. 
VOLATILE OILS. 
Oil of citronella, oil of pennyroyal, and similar substances are used 
frequently to rub on the face and hands and to place on the bed- 
clothes at night, and have some effect in keeping away mosquitoes. 
They evaporate rapidly, however, so that their benefits are only 
temporary. None of them will last through the night. 
ISOLATION AND PROTECTION OF PERSONS SUFFERING WITH MALARIA. 
Any prisoner who is suffering with symptoms which may reason- 
ably be ascribed to malaria should be isolated at once and carefully 
protected from mosquitoes by mosquito bars. This will prevent 
mosquitoes which are not infected from biting the patient and so 
becoming infected and capable of transmitting the disease to others. 
Mosquitoes can not transmit malaria without first biting a person 
1 Rosenau, " Preventative Medicine and Hygiene," p. 205. 
