MALARIA. 191 



thence, by way of the veneno-salivary duct in the hypopharynx, they are 

 introduced into the circulation of the person bitten by the mosquito, 

 and start a nonsexual cycle. As the sexual life takes place in the 

 mosquito, this insect is the definitive host man is only the interme- 

 diary host. 



There are three species of malarial parasites: (i) the Plasmodium 

 vivax, that of benign tertian cycle, forty-eight hours; (2) the Plasmo- 

 dium malariae, that of quartan cycle, seventy-two hours; and (3) the 

 Plasmodium falciparum, that of aestivo-autumnal or malignant tertian- 

 cycle of forty-eight hours. 



Variations in cycles may be produced by infected mosquitoes biting 

 on successive nights, so that one crop will mature and sporulate twenty- 

 four hours before the second. This would give a quotidian type of 

 fever. In aestivo-autumnal infections anticipation and retardation in 

 the sporulation causes a very protracted paroxysm, lasting eighteen to 

 thirty-six hours; this tends to give a continued fever instead of the 

 characteristic type. 



UNSTAINED SPECIMEN (FRESH BLOOD). 



