Proceedings of Eighth Annual Meeting 121 



is also highly toxic to protozoa and algae, as well as most varieties of 

 common grasses encountered in Panama. The algacidal and herbicidal 

 properties of this larvicide are of frequent use in mosquito eradication. 

 The disadvantages of this larvicide are: 



1 — It does not emulsify and is inert in brackish water. This is a serious 



disadvantage because many Anopheles breed in brackish water and 

 Culex breed in salt-water marshes and pools. This defect, however, is 

 shared by all the commercial larvicides tested on the Isthmus. 



2 — The pure larvicide deteriorates upon exposure to the air and must be kept 



in drums, barrels, and other tightly closed containers. 



3 — It rapidly loses its toxicity after mixing with water containing algae and 



other organic matter. After 24 hours its toxicity is so far diminished 

 that it is practically non-toxic from the standpoint of field practice. 



The toxic action of this phenol-resin larvicide upon mosquito 

 larvae is probably due to the action of its phenol content upon the 

 protoplasm of the larvae, probably intensified by the fact the phenol 

 is in emulsion. , 



The Panama Larvicide, according to many authorities is very 

 effective, but its use is limited to fresh water control. 



Nitre Cake, a by-product of the manufacture of explosives, is a 

 grayish hygroscopic salt, consisting of anhydrous sodium sulphate 

 and acid sodium sulphate. Dr. R. C. Deriveaux used nitre cake 

 during the Crossett, Arkansas, anti-malarial campaign and found 

 it to be lethal to larvae and pupae and to prevent the development of 

 ova in a dilution of i 400. He treated five barrels, using one pound 

 of the cake, stirred into solution, to the fifty gallon barrel. No 

 breeding occurred in any of the barrels during the season. 



R. E. Tarbett, found niter cake very effective for treating fire 

 barrels. He dosed each barrel v^ith three pounds of the cake, 

 which was added dry, without any attempt at pulverizing or making 

 into a solution. Fifteen hundred barrels were dosed and no breed- 

 ing occurred in any of the barrels during the season. It was found 

 that niter cake in a dilution of i 400 killed larvae in fifteen to 

 twenty minutes, but did not affect pupae. Tarbett also dosed a 

 catch basin, using ten pounds of the cake to the basin and no breed- 

 ing occurred. 



Dr. Headlee experimented with nitre cake and found that a 

 I :iooo solution was barely sufficient to destroy the larvae of Culex 

 pipiens in two days time, but that stronger solutions, i :ioo destroyed 

 this species readily and remained effective for 21 days or longer. 

 A solution (6 grams of nitre cake to looocc of water testing 7% 

 saHnity) was found to destroy the larvae of Aedes soUicitans, but 

 required three days to accomplish the result. 



