PROPHYLAXIS 



1207 



of the density surrounding that area. A square one mile wide will 

 have a central density of 2 per cent., at a quarter of a mile from 

 the boundary 11 per cent., and at the boundary 50 per cent, of the 

 surrounding density. No experiments have, however, been carried 

 out to determine whether these assumptions are correct. 



There is, however, no doubt that anopheline reduction leads to 

 the reduction of malaria. The work done under Ross's direction 

 at Ismailia proves this, for the cases of malaria were reduced from 

 1,551 in 1902 to 37 in 1905, and these latter Were all relapses. The 

 cost of this is given as 50,000 francs for drainage and filling up of 

 pools, with a yearly expenditure of 18,300 francs, which worked 

 out at 23 francs per head of population. 



Travers and Watson at Klang and Port Swettenham, in the 

 Malay States, by similar methods reduced the cases of malaria 

 admitted into the hospitals from 610 in 1901 to 23 in 1905, while 

 the cases from the surrounding district in which no antimalarial 

 methods were employed were 197 in 1901 and 353 in 1905. The 

 children found infected in the two towns in 1905 amounted to 

 0*5 per cent, of those examined, while in the surrounding district 

 they were more than 23 per cent. The financial saving is also 

 shown by the fact that Government employes in 190 1 obtained 

 236 sick certificates, amounting to 1,026 days' leave, and in 1905 

 only 4, amounting to 30 days' leave. The cost to the end of 1905 

 was £10,100, with a yearly expenditure of £410. The cost up 

 to the end of 1905 worked out at £1 49. per head of the popu- 

 lation. 



Similar work has been done in Hong Kong by Dr. Thompson. 



In Panama, under American rule, the measures taken are very 

 elaborate and systematic, because the sanitarian is given a free 

 hand, and economy is not considered where health is in question, 

 with the result that malaria and yellow fever have disappeared. 

 There can therefore be no doubt that the destruction of anophe- 

 lines will lead to the diminution of malaria. 



The Insect. — ^The measures which are used may be classified into 

 those directed against the insect and those against the larvae. With 

 regard to the insects, fumigation with some substance such as 

 sulphur (2 pounds to be burnt for every 1,000 cubic feet of space) 

 or pyrethrum will Stupefy them and cause them to fall to the ground, 

 when they can be swept up and burnt. This is useful in dealing with 

 individual houses prior to residing therein. The insects may also 

 be destroyed in houses by the use of the hand-net as advocated 

 by Ross and Gorgas, while the use of a hand-fan is also recom- 

 mended. Mosquito traps have also been used and Giemsa's 

 pyrethrum sprays. 



Spraying is specially useful for outhouses, stables, etc., and in 

 addition to the pyrethrum spray weak formalin may be used. 



The Larva. — It is, however, against the larvae that measures are 

 most easily ta'ken, and these include: — 



