April, '12] MOSQUITO DISCUSSION 141 



imperative. It is obviously impracticable to thoroughly clear and 

 control square miles of territory, covered with heavy timber and soon 

 to be buried beneath the waters of the lake, but until the permanent 

 level is reached the uncleared and shallow margins of the lake will 

 supply myriads of mosquitoes to the adjacent regions. 



In conclusion I would emphasize the fact that the sanitary organiza- 

 tion of the Isthmian Canal Zone has prosecuted the work of mosquito 

 control in the face of great difficulties of climate and situation. 

 Constant changes in physical conditions have necessitated prompt and 

 energetic action in the contrivance and application of relief measures. 

 Heavy demands have been made upon the resourcefulness, ingenuity, 

 devotion and physical endurance of the personnel, and upon their 

 response to the call has largely depended the high success attained. 



President F. L. Washburn: Any discussion on this paper, of the 

 utmost interest to us all? Doctor Schwarz. 



E. A. Schwarz : As with everyone that has visited the Canal Zone, 

 I cannot but admire the efficacy of the work done by the sanitary 

 department of the Canal Zone Commission in cleaning up the mos- 

 quitoes from the country so that yellow fever is practically unknowTi 

 and malaria under almost perfect control. The common non-patho- 

 genic mosquitoes are not obvious at all during the dry season of the 

 year but as soon as the summer rains commence, they are just as 

 common all over the Canal Zone as elsewhere. On a short trip up 

 the rapid flowing Chagres River, I was not aware of the presence of any 

 mosquitoes and at Porto Bello up to which place the operation o fthe 

 sanitary department has not j'et extended and where there are many 

 clear mountain streams, I was never seriously troubled by the attacks 

 of mosquitoes. 



President F. L. Washburn: Any other remarks upon this paper? 



Henry Skinner: Mr. President, the speaker said something about 

 Anopheles breeding in depressions. I just wanted to find out whether, 

 in a tropical country, the water would remain in such long enough to 

 enable the mosquitoes to undergo their transformations. It might 

 be a matter of some little importance to find that out. 



Allen H. Jennings: A depression will be filled many times before 

 it is emptied, and where the soil is fairly impervious, as it is in many 

 cases, the water \n\\ remain an ample time; in fact, far more than 

 long enough for the transformations to take place. 



Frederick Knab: One little point I would like to call attention 

 to, and that is the fact that the habits of the different species of Ano- 

 pheles have everything to do with their relation in carrying malaria. 

 Now, Anopheles alhimanus, which is the principal malaria carrier if 

 I have understood Mr. Jennings correctly, is to a certain extent domes- 



