126 AGRICULTURAL EXPERIMENT STATION. 



may be practically ignored except within actual city or town 

 limits. 



The Anopheles or malaria carriers have no breeding places 

 that are peculiar to themselves alone. Hence a campaign against 

 them is bound to hit practically all the local breeders, while a 

 campaign against all local breeders is ecjually certain to reach 

 Anopheles. But, while the species do occur everywhere they 

 are much more likely to occur with sylvestris and especially in 

 swamp areas and sluggish streams. Syh'estris, as has been 

 shown, flies for some distance, hence a community desiring ex- 

 emption must seek out its chief breeding areas for at least a mile 

 from the point to be cleared. 



Oil kills Anopheles as readily as it does Culex, but it is not 

 always so easy to get it where it is needed. Oiling a stream of 

 any size creates an offense out of all proportion to the results to 

 be obtained, and the results are bound to be imperfect because the 

 insects retreat to sheltered situations where the oil does not readily 

 penetrate, and where the film is broken against the grass and 

 other debris. Even a slow current will carry off the oil film in 

 a few hours, if not, indeed, in a comparatively few minutes. 

 The same difficulty in doing effective work with oil applies to 

 swamp areas more or less choked with vegetation. Yet it would 

 be possible, of course, to do real thorough work if time, material 

 and labor were no objects. The chief objection to its use is 

 really its temporary character. It must be done several times 

 during the season and at the beginning of the season thereafter 

 absolutely no progress has been made and the work ahead is prac- 

 tically the same as was done the year before. The expense is a 

 continuous one and equally great each year, while with permanent 

 improvements such as result in the eradication of a breeding place 

 though the initial expense be greater, the result is continued ex- 

 emption without further outlay except for maintaining conditions. 



