106 BULLETIN 414, U. S. DEPARTMENT OF AGRICULTURE. 
being about 1.4 cents. But it has the distinct advantage of not 
affecting the fertilizing value of the manure even when used in 
excessive amounts. 
Mosquitoes. 
It is now definitely known that in nature malaria is transmitted 
only by the sting of certain species of mosquitoes, and the most suc- 
cessful means of avoiding this disease is to provide protection from 
mosquitoes. 
When convict camps are located for an entire summer season in 
regions where mosquitoes abound, it may be found profitable to strike 
at the mosquitoes by destroying their breeding places in so far as this 
is practicable. 1 The antimosquito measures generally employed are 
briefly described by the United States Public Health Service as 
follows : 
(a) Regrading and training of streams, creeks, or similar natural water courses so 
as to favor a free current. 
The shallow grass-grown margins of streams, ponds, or any bodies of water must be 
cleared and the banks made with a clear-cut edge in order that any top-feeding min- 
nows present may have a clear field for their activity and that this field may be 
extended. 
(6) Drainage for the removal of standing water or to produce a movement of water 
unfavorable to mosquito breeding. Ditches should be as few and as short as possible 
and so constructed that any water present will be confined to a narrow channel. Open 
ditches must be kept free of grass, debris, or any other obstructions. They may be 
made permanent and easy of maintenance by lining with cement, stone, or wood. 
Ditches as ordinarily used should have a bottom not over 8 inches wide and the 
sides sloping. £ 
Subsoil tile drains, while more costly, are more effective. 
(c) Filling in of places which are too low to drain or which can not be drained eco- 
nomically. For this purpose any available porous material, such as ashes, sawdust, 
or shavings, may be employed. When using sawdust or shavings, such material should 
extend 6 inches or more above high water which follows a heavy rain. 
(d) Oiling and larvicides. Oil may be applied by the use of (1) a garden watering- 
pot; (2) a knapsack sprayer; (3) a drip can for intermittent or continuous oiling regu- 
lated to deliver 18 to 20 drops of oil per minute. The bottom of the drip can should be 
about 4 feet above the level of the water surface; (4) an oil-saturated bundle of cotton 
waste. This is to be anchored into place and will serve for about one week, (e) Natu- 
ral enemies. Stocking with top-feeding minnows is a measure applicable in certain 
ditches, ponds, swamps, streams, and many other bodies of water. 
For camps which change their location every few weeks the fore- 
going measures may be too elaborate for use. It should be remem- 
bered, however, that mosquitoes can not live in the hot sun and that 
the clearing away of high grass and underbrush from the surround- 
ings of the camp will aid materially in diminishing their number. All 
barrels and tubs used for the storage of water should be covered 
tightly with thicknesses of burlap, sheeting, or cheesecloth, held in 
place by well-fitting hoops, and should be fitted with spigots so that 
i Reprint No. 272, From the Public Health Reports, U. S. Public Health Service, Apr. 30, 1915. 
