54 MOSQUITO ERADICATION 



total number of persons infected who had not been able, either 

 by natural resistance or by the use of quinine, to banish the Plas- 

 modia from their systems. Thus at Roanoke Rapids, as will 

 be seen later, the blood tests in the fall showed 13.75 per cent of 

 the total population infected with plasmodia; during the mosquito 

 season, however, about 75 per cent of the total population was 

 infected, according to the health officer. 



It should also be borne in mind, in interpreting the percentages 

 of reduction of persons reporting infection or illness (history index) 

 and of physicians' calls, etc., that what may seem like a heavy 

 remaining infection, despite a considerable reduction due to 

 control work, may be only recurrences of former infection. As 

 intimated in Chapter I, chronic cases may regain their acuteness 

 when the bodily resistance becomes disturbed or weakened, 

 without there being a new infection at all. Thus, the work may 

 be very effective and, indeed, prevent any new infection at all, 

 despite the fact that the history index and the records of physi- 

 cians' calls may still show quite a percentage of cases. These 

 chronic cases however, show a marked reduction year by year 

 when the work is kept up. 



Owing to the difficulty of ascertaining in cases of protracted 

 illness whether the patient is suffering from one chronic infection 

 or repeated new ones, it has been found generally that compari- 

 sons of physicians' calls gives a better idea of the effectiveness of 

 the campaign than comparisons of cases. Just what the relation 

 of calls to cases may normally be is not definitely known. It is 

 believed, however, that in general, especially where the sickness 

 is wide-spread, physicians do not average more than two calls to 

 a case, and frequently not that. 

 EARLY UNITED STATES MALARIA CONTROL DEMONSTRATION 



Roanoke Rapids, N. C, is a cotton-mill town in the northern 

 part of the state, having a population, including two nearby 

 mill villages, of approximately 4,100 in 1913. During the 

 summers of 1910, 1911, 1912 and 1913, according to the health 

 officer, 75 per cent of the people of Roanoke Rapids suffered 

 from malaria. During the same periods, this physician's visits 

 on account of malaria alone averaged about 50 a day. 



Anti-mosquito work was begun under auspices of the U. S. 

 Public Health Service in January, 1914 and continued until 

 the end of the season of 1916. The following table 1 shows the 



1 " Demonstrations of Malaria Control," U. S. Public Health Service, 1918. 



