120 DEAGON FLIES A^S. MOSQUITOES. 



larvae in the water and Ijy entanglement effect their de- 

 struction before they could rise to the surface for the 

 respiration of air. This suggestion appears to me im- 

 portant, and I am inclined to agree with Mr. Gratacap that 

 the vast numbers of the fronds of Oscillatoria in the Cen- 

 tral Park lakes have had a deterrent effect upon the prop- 

 agation of mosquitoes in those localities. The requisition 

 here is a largely disseminated mass of algse, which, in such 

 rod-like forms as Oscillatoria, will float through the water 

 and by its intermixed and diffused stipes embarrass the 

 development and movements of the mosquito larvae. I 

 cannot lay especial stress on this suggestion, but regard it 

 as a very interesting field for practical experiment. 



Artificial Remedies. 



The second class of remedies are those which involve 

 the use of artificial means, chemical, physical, or mechani- 

 cal, and which ingenuity has proven to be effective. They 

 are, first, those which aim directly at effecting the destruc- 

 tion of the mosquito ; and, second, those which are simply 

 deterrent or protective to the individuals attacked by 

 mosquitoes, and therefore of limited and strictly adventi- 

 tious usefulness. 



The use of coal oil in swamps, by filming the ground, 

 odorizing the air, and floating U23on the surface of the 

 water itself, is a very practical and energetic remedy. It 

 has its disadvantages, and I recall the principle I laid 

 down in the '' Discussion of the Problem," that no reme- 

 dy should be recommended which replaced the scourge we 

 endeavor to eject by an obnoxious substitute. Yet, in 

 many places removed from general habitations, this rem- 

 edy can be safely employed. It acts destructively upon 



