PETROLEUM 381 



not only mosquito larvae, but all other animal life in the water. It is used in 

 cesspools and receptacles of that kind, and it has found wide application in the 

 anti-mosquito work on the Isthmus of Panama. 



CACTUS PASTE. 



We have already spoken of the use of certain substances for forming so dense 

 a covering over the surface of the water as to exclude mosquito larvje from access 

 to air, thus bringing about their destruction. A method of bringing about this 

 result is described by Consul Wm. H. Bishop, of Palermo, Sicily, in the Monthly 

 Consular and Trade Reports, No. 331, April, 1908, in which he quotes from an 

 account of the experiments made by the Chief of the Sanitary Service at Graboon, 

 French Africa, with cactus as a substitute for petroleum in the extermination 

 of mosquitoes in warm climates. Beyond this account by Mr. Bishop, we have 

 no further information of this remedy : 



" The thick, pulpy leaves of the cactus, cut up in pieces, are thrown into water 

 and macerated until a sticky paste is formed. This paste is spread upon the 

 surface of stagnant water, and forms an isolating layer which prevents the 

 larvae of the mosquitoes from coming to the top to breathe and destroys them 

 through asphyxiation. It is true that petroleum can do the same service, but 

 in warm climates petroleum evaporates too quickly and is thus of little avail. 

 The mucilaginous cactus paste, on the contrary, can hold its place indefinitely, 

 lasting weeks, months, or even an entire year ; and the period of the development 

 of the larvae being but about a fortnight, it has the most thorough effect.^' 



PETROLEUM. 

 This substance has been more extensively used in the United States than else- 

 where and it is better understood in this country. In choosing the grade of the 

 oil, two factors are to be considered. First, it should spread rapidly ; second, it 

 should not evaporate too rapidly. The heavier grades of oil will not spread 

 readily over the surface of the water, but will cling together in spots and the 

 coating will be unduly thick. The rapidity of spread of film is also important. 

 Eonald Eoss, in his '^ Mosquito Brigades," pp. 34 to 35, makes the following 

 statement : 



" Mr. Hankins of Agra informs me that the addition of Amyl alcohol greatly 

 expedites the formation of the film; and it is very necessary to obtain a film 

 which makes its way between the stalks and leaves of water weeds." 



Early in the course of anti-mosquito work in the United States careful ex- 

 periments were made by Mr. W. C. Kerr, in the work of the Eichmond County 

 Club, on Staten Island. He tried several grades of oil and found a low grade of 

 oil known as " fuel oil " to be best adapted to the work. Of the oils which he 

 tried, some contained too much residuum of a thick nature, which appeared as a 

 precipitate and could scarcely be pumped, some were too thick in July weather 

 and could not be pumped at all, while others were limpid, easily handled, made 

 a good uniform coating on the ponds, and were very effective. So long as oil 

 flows readily and is cheap enough the end is gained, provided it is not too light 

 and does not evaporate too rapidly. The grade known as light fuel oil was recom- 

 mended by one of the writers to the U. S. Army workers in Cuba, at the close of 



