384 MOSQUITOES OF NORTH AMEEICA 



PHINOTAS OIL. 



In the Panama work, as previously stated, pliinotas oil is used, and has been 

 found to have the following advantages over crude oil : It acts as a poison and 

 kills the larvge very rapidly. It brings the larvse out of their hiding-places at 

 once, and is useful as an aid in the detection of the presence of mosquito larvae. 

 It is found also that in continuous heavy rains the larvae are killed by the 

 phinotas oil before the rain dilutes the treated water to any great extent. They 

 find, however, that phinotas oil has certain disadvantages : It kills fish in a 

 solution of 1 to 5000, and it loses its efficiency very soon after application, so 

 that eggs may be laid upon the treated water and the larvae develop. Colonel 

 Gorgas points out that there is considerable variation in the quality of this 

 preparation, as shipped to the Isthmus. Some will kill larvse quickly in a solu- 

 tion of 1 to 3000 parts of water, while other lots require for the same results 1 

 part to 1000. 



THE IDEAL LARVICIDE. 



Colonel Gorgas has published the following list of desiderata for the perfect 

 larvicide for use in the tropics, agreeing with the opinion expressed by Eonald 

 Eoss when he returned from his first visit to Africa, that nothing as yet known 

 is perfectly satisfactory : 



" (a) Low ultimate cost. 



" (b) Ability to affect and kill mosquito larvae promptly, the more rapidly the 

 better. It must be effective in moving water as well as in still water. 



" (e) Ability to form a solution with water and to thoroughly diffuse and mix 

 with all the water of a small pond if applied only to one part thereof. Also the 

 substance must not lose it larvacidal properties for a week or more after its 

 application. The longer it will retain its larvacidal properties, after it has 

 been placed in the body of water, the more valuable it will be. 



"(d) Ability to diffuse in water and through all parts of a body of water such 

 as in a pond containing grass, water lilies, other aquatic vegetation, and vege- 

 table debris. 



" (e) Ability to kill green algae promptly. 



" (f ) A concentrated larvacide is necessary so that one part of it to five thou- 

 sand or more parts of water will promptly kill mosquito larvte and pupae. 



" (g) Non-poisonous to human life or animals when taken in a strength of 1 

 to 1000 and accidentally used as drinking water. 



" (h) That it have the property of discoloring the water to which it is applied, 

 or of giving off sufficient odor to induce persons not to use water containing it 

 in solution for drinking purposes. 



" (i) That the odor, if present, be not so obnoxious as to make its presence in 

 water in ponds or streams near habitations undesirable. 



" (j) That it shall have a safe flash test and be nonexplosive. 



" (k) That it shall be sufficiently stable so that it may be kept ' stand- 

 ardized.' " 



LARVICIDE OF THE ISTHMIAN CANAL COMMISSION. 



In his " studies in Eelation to Malaria," Dr. Samuel T. Darling, of the 

 Isthmian Canal Commission, gives the following account of experiments with 

 larvicides : 



