130 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 w^est 

 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. 



Mosquitoes 



It may be well at this point to give a brief outline of the 

 life-history of mosquitoes, especially those concerned in 

 the transmission of malaria and of yellow fever. 



Mosquitoes reproduce themselves by means of eggs 

 which the female lays on the surface of stagnant water. 

 After several days the eggs hatch out into what are called 

 "wrigglers," which live in the water and can readily be 

 seen with the naked eye. After a day or two the wriggler 

 changes into a pupa, and from this, after a further inter- 

 val, the winged insect, the mosquito, emerges. It is 



