THE MALARIAL MOSQUITO iii 



Within i,ooo yards it diminished to 2*6 per cent. (Watson). 



At the edge it was 59 per cent. 



Fry found it to be 2s per cent, at 200 yards away and nil at one mile 

 distance. 



Mosquitoes fly readily for a Cjuarter of a mile, but half a mile 

 appears to be beyond the normal distance of flight. A gentle breeze 

 will carry them a distance of one and a half miles. 



100,000 mosquitoes per 100 yards square was once worked out to 

 be an average number present. 



Anopheles are not hungry for twelve to twenty-four hours after 

 being hatched out or after laying eggs. 



On an average only one out of forty-eight of all females ever have 

 the chance of carrying malaria even in a malarial district (Ross). 



The cost of a new hospital wOuld often suffice to prevent more cases 

 of sickness than are treated in it, and the cost of invaliding would often 

 suffice to prevent the disease which caused it. 



THE MALARIAL MOSOUITO. 



The knowledge of these mosquitoes is so extensive that special 

 works must be consulted for details. A resume only of the outstanding 

 facts can be attempted here. 



The four great families of the Xematocera, order Diptera, which 

 are of interest to the medical officer are the — 



(i) Culicidas, or mosquitoes. 



(2) Psychodidfe or moth-like midges, containing the notorious 

 Phlebotomus. 



(3) Chironomid^e, or midges. 



(4) Simulidi^e, all the species of which are extremely bloodthirsty. 



FAMILY CULICIDiE. 



They are distinguished from the midge-like flies by : — 

 (i) The venation. The costal vein runs all round the edge of the 



wing. 

 ,, first vein is very long. 

 ,, second bifurcates. 



,, third is very short and goes off the second 

 at right angles. 



ij 



fourth 



both bifurcate. 



,, fifth 

 ,, sixth is simple and short. 

 (2) The close fringe of scales on the posterior border of the wings. 



