128 APPLIED BACTERIOLOGY FOR NURSES 



tained by bringing together methylene-blue and water- 

 soluble eosin; the resulting powder is soluble only in 

 alcohol; it stains the parasites blue, red blood-cells a 

 deep pink, and white blood-cells pale pink with blue 

 nucleus. 



Apparently there exists a slight natural immunity 

 to malaria; occasionally a few residents in malarial dis- 

 tricts escape infection. Also a partial immunity is 

 acquired by some individuals who have passed through 

 one or more infections. Thus the negroes on the west 

 coast of Africa are less severely attacked than Euro- 

 peans who go to live there, and Koch has attributed 

 this to their having acquired a partial immunity during 

 childhood. 



The malarial parasites are actively destroyed by 

 quinin, arsenic, and certain other substances. In the 

 campaign in this climate against malaria it is well to 

 direct attention also to suppressing the mosquito 

 nuisance, and, hand in hand with that, to kill the malarial 

 parasites in their human hosts by means of quinin. 



YELLOW FEVER 



Although the specific organism of yellow fever has not 

 yet been identified, it may be well to mention the disease 

 here, because, like malaria, it requires a particular kind of 

 mosquito (Stegomyia calopus) for its transmission from 

 man to man. The disease is. not conveyed by fomites. 

 The bite of an infected mosquito does not become infectious 

 until twelve days after it has bitten the first patient. 

 There is a definite time between the bite of the mosquito 

 and the infectivity of the patient's blood (average five 

 days), and a definite time the blood remains infective 



