102 PREVENTIVE MEDICINE 



(5) As a general rule for practical purposes, if the area of opera- 

 tions be of any considerable size, immigration will not very mate- 

 rially affect the result. 



In conclusion, it must be repeated that the whole subject of 

 mosquito-reduction cannot be scientifically examined without 

 mathematical analysis. The subject is really a part of the mathe- 

 matical theory of migration a theory which, so far as I know, 

 has not yet been discussed. It is not possible to make satisfactory 

 experiments on the influx, efflux, and varying density of mosquitoes 

 without such an analysis and one, I may add, far more minute 

 than has been attempted here. The subject has suffered much at the 

 hands of those who have attempted ill-devised experiments without 

 adequate preliminary consideration, and whose opinions or results 

 have seriously impeded the obviously useful and practical sanitary 

 policy referred to. The statement, so frequently made, that local 

 anti-propagation measures must always be useless, owing to immi- 

 gration from outside, is equivalent to saying that the population of 

 the United States would remain the same, even if the birth rate 

 were to be reduced to zero. In a recent experiment at Mian Mir in 

 India the astounding result was obtained that the mosquito-density 

 was, if anything, increased by the anti-propagation measures 

 which is equivalent to saying that the population of the United 

 States would be increased by the abolition of the birth-rate. In the 

 mean time, I for one must continue to believe the somewhat self- 

 evident theory that anti-propagation measures must always reduce 

 the mosquito-density even if the results at Havana, Ismailia, 

 Klang, Port Swettenham, and other places are not accepted as 

 irrefragable experimental proof of it. 



