636 MALARIAL FEVER 



after becoming free are destroyed by leucocytes, but if measures 

 are taken to prevent the presence of these, other generations of 

 growth may be obtained in similarly prepared tubes of blood 

 with sufficient serum. The parasites nourish only in the super- 

 ficial layers of the sedimented corpuscles, and the most suitable 

 temperature is 40-41 C. These results have been confirmed 

 by Thomson and M'Lellan. 



General Considerations. The development of the malarial 

 parasites in the mosquito and infection of the human subject 

 through the bites of this insect, have, by the work of Ross and 

 others, as detailed above, become established scientific facts. 

 These facts, moreover, point to certain definite methods of pre- 

 vention of infection, which have to a certain extent already been 

 practically tested. The extensive observations recently carried 

 out go to show that all the mosquitoes which act as hosts of the 

 parasite belong to the genus anopheles, of these there are a 

 large number of species, and in at least eight or nine the 

 parasite has been found. Some of these anopheles occur in 

 England, especially in regions where malaria formerly prevailed. 

 The opportunity for infection from cases of malaria returning 

 from the tropics to this country thus exists, and such infection 

 has occurred. The breeding-places of the insects are chiefly, 

 though not exclusively, in stagnant pools and other collections 

 of standing water, and accordingly the removal, where practicable, 

 by drainage of such collections in the vicinity of centres of popu- 

 lation, the covering in of wells, etc., and the killing of the larvae 

 by petroleum sprinkled on the water, have constituted the most 

 important measures in localised areas. This procedure has been 

 carried out in various places, for example, in Freetown and 

 Ismailia, with marked success. On the other hand, where there 

 are large populous areas, as in India, it has been found almost 

 impracticable to carry out these measures with any success. 

 Another measure is the protection against mosquito bites by 

 netting, it being fortunately the habit of the anopheles rarely to 

 become active before sundown. The experiments of Sambon 

 and Low in the Campagna proved that individuals using these 

 means of protection may live in a highly malarial district with- 

 out becoming infected. The administration of quinine to 

 persons living in highly malarial regions, in order to prevent as 

 well as to treat infection, has also been recommended and 

 carried out, and the general agreement appears to be that in 

 India the properly controlled administration of quinine must, 

 in the meantime at least, be the chief means of combating the 

 disease. Jn the tropics the natives in large proportion suffer 



