106 BULLETIlSr 414, XJ. S. DEPAETMEISrT OF AGEICULTUEE. 



being about 1.4 cents. But it has the distinct advantage of not 

 affecting the fertihzing 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.^ The antimosquito measures generally employed are 

 briefi}^ 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. 



(&) 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. AU 

 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 



1 Reprint No. 272, From the Public Health Reports, U. S. Public Health Service, Apr. 30, 1915. 



