6 9 



CHAPTER VI. 

 PROPHYLAXIS. 



Etiology. It is not necessary to do more than allude 

 to the older hypotheses as to the causation of malaria. 

 These were mainly founded on the belief that emanations 

 from decomposing vegetables or from soil or rocks such as 

 granite caused the fever. These emanations were known 

 as " miasmata," and were believed to rise only a short dis- 

 tance from the ground during the night and to be dissi- 

 pated by the sun. It is from this hypothesis that the 

 term for the disease, malaria, is derived. These observa- 

 tions as to the occurrence of malaria are in many cases 

 more readily explained now that it is known that the 

 disease is carried by mosquitoes. 



We now know that malaria is a parasitic disease, and 

 that the parasites are conveyed from man to man by 

 certain species of mosquitoes. 



As far as we know these parasites can only exist in 

 man and mosquitoes. Seasonal variations occur in most 

 places, due (i) to the variations in the meteorological 

 conditions affecting the multiplication, breeding, and 

 prevalence of suitable mosquitoes; and (2) to the tem- 

 perature being suitable for the development of the malaria 

 parasites in these cold-blooded definitive hosts. Local 

 variations are often due to the prevalence and proximity 

 of suitable warm-blooded hosts human beings the 

 intermediate hosts of the malaria parasites. Native 

 children and bodies of new-comers from non-malarial 

 countries are the most important carriers, or reservoirs, 

 of the parasites to consider. 



Malaria can be propagated from man to man by trans- 



