312 The Control of Mosquitoes 



frequent inspections to detect sagging, etc., which 

 tends to collect water. In practice it was almost 

 impossible to maintain existing roof gutters on 

 private residences in a self-draining condition 

 except those placed over entrances and not exceed- 

 ing eight feet in length. 



From time to time a wooden vessel holding a 

 little clean water is exposed in a position convenient 

 for ovipositing. The vessel is observed daily for a 

 week or two to detect the presence of larvae in a 

 given locality and reach a fairly definite con- 

 clusion regarding their presence or absence. 



The methods adopted to keep the ntimber of 

 Aedes calopus on the Isthmus below the infective 

 minimum and the results that have been accom- 

 plished are due to the thorough and painstaking 

 application of now well-known measures. It has 

 been asserted that the eradication of such a pro- 

 lific insect species as the Aedes calopus is impossi- 

 ble. The senior author believes it possible; but 

 for the practical purposes of the prophylaxis of 

 yellow fever, entire eradication of Aedes calopus 

 is desirable but not a necessity. What is needful, 

 is to keep their number in a given locality below 

 that required to propagate the disease. It is dif- 

 ficult to determine what this number is. It would 

 differ according to the number of fever cases 



