PETROLEUM 381 
not only mosquito larve, 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 larvee 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 Gaboon, 
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 
larvee 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 larvee 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. 
Ronald Ross, 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 Richmond 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 
