PREVENTION 165 



in a few months by destroying the parasites in man by whole- 

 sale " quininization." In most places, however, the difficulties 

 connected with this method of extermination are even greater 

 than those associated with its alternative, the destruction of 

 malarial mosquitoes. The relation of partially or entirely im- 

 mune " carriers " to the spread of malaria is of extreme impor- 

 tance and is usually greatly underestimated. The number of 

 such apparently healthy carriers in malarial districts is astonish- 

 ingly large. Eradication of malaria by attacking it in man would 

 entail the persistent and thorough quinine treatment of all these 

 carriers as well as of patients. 



Undoubtedly in practically every case, if accompanied by as 

 extensive a use of quinine as is possible, eradication of malarial 

 mosquitoes is the most effective and most permanent preventive 

 measure. A discussion of methods of reducing and controlling 

 such mosquitoes will be found on pages 455^62. 



Complete extermination of malarial mosquitoes is not necessary 

 to reduce or even to eradicate malaria entirely. Ross has shown 

 by mathematical computation that a relatively high number of 

 malarial mosquitoes per person is necessary in a community to 

 propagate malaria successfully. A small deviation above or 

 below a certain number of malarial mosquitoes, probably between 

 40 and 60 per person during a month, a deviation too small to 

 be detected readily, will mean the difference between an ulti- 

 mate extermination of the disease and its permanent establish- 

 ment. Ross also shows that the relation between the amount 

 of malaria in a given region and the number of malarial mosqui- 

 toes is so definite that it can be mathematically computed. 

 These facts are of importance in the fight against malaria sines 

 they demonstrate to us that we do not have to exterminate 

 totally even the malaria-carrying species of Anopheles in order 

 to exterminate malaria, and our task becomes much less difficult. 

 By this partial extermination some of the most malarial districts 

 in the world have been practically freed. Up to 1900 over 16,000 

 deaths a year from malaria occurred in Italy; now they may be 

 counted in hundreds. One of the first demonstrat'ons of what 

 could be accomplished by mosquito extermination was made by 

 Major Ross in 1902 at Ismailia on the Suez Canal where from 

 1100 to 2500 cases of malaria occurred annually in a population 

 of less than 10,000. Four years later not a single new case 



