The Isthmus in 1904 25 



are always to be found, and yellow fever and smallpox 

 will occur when favorable clinical material presents 

 itself, unless proper precautions are taken. • 



In order to obtain certain data concerning 

 malaria transmission, an experimental station was 

 established at Ancon, and non-immunes were 

 isolated there for the experiments, but so many 

 Anopheles al imanus were present that it was 

 extremely difficult to prevent natural malaria 

 transmission. 



Low lying flat areas occurred for a distance of 

 six miles inland from the Pacific terminal and to 

 a still greater distance from the Atlantic Coast. 

 Much of this area was afJected by the highest 

 tides, and Anopheles larvs were present in streams 

 on steep hillsides as well as on the lowlands. 



The preliminary survey showed that Anopheles 

 and other mosquitoes were present near all the 

 camps, but the impassable jungle made it impos- 

 sible to determine the extent of the propagation 

 areas and it was evident that considerable clearing 

 would have to be done to obtain the data desired. 

 Innumerable small puddles were everywhere, and 

 their possibilities as mosquito producers depended 

 upon the frequency of the successive showers. The 

 rapidity of growth of vegetation was remarkable, 

 and showed that its control would be an important 



