THE MALARIAL PARASITE. 637 



bodies in the absence of methods for obtaining each species sepa- 

 rately, in pure cultures. 



Thayer and Hewetson, in their admirable monograph on the 

 Malarial Fevers of Baltimore (1895), in which they give an ac- 

 count of six hundred and sixteen cases observed by themselves, 

 have summarized their observations relating to the parasite as 

 follows : 



" We have distinguished three varieties of the malarial par- 

 asite : 



"1. T]ie tertian parasite. 



" 2. The quartan parasite. 



" 3. Tlie cestivo- autumnal parasite. 



" (1) The tertian parasite requires about forty-eight hours to 

 accomplish its complete development, and is associated with 

 relatively regular tertian paroxysms, lasting on an average be- 

 tween ten and twelve hours, associated, almost always, with the 

 three classical stages chill, fever, and sweating. Frequently, in- 

 fection with two groups of tertian organisms gives rise to quo- 

 tidian paroxysms ; rarely, infection by multiple groups of organ- 

 isms gives rise to more irregular, subcontinuous fevers. 



" (2) The quartan parasite is an organism requiring about 

 seventy-two hours for its complete development. It is rare in 

 this climate, and is associated with a fever showing regular 

 quartan paroxysms, similar in nature to those associated with 

 the tertian organism. Infection by two groups of the parasite 

 causes a double quartan fever (paroxysms on two days, intermis- 

 sion on the third). Infection with three groups of the parasite 

 is associated with daily paroxysms. 



" (3) The cestivo-autumnal parasite passes through a cycle of 

 development, the exact length of which has not as yet been de- 

 termined ; it probably varies greatly, from twenty- four hours or 

 under to forty-eight hours or more> But few stages of develop- 

 ment of the parasite are found, ordinarily, in the peripheral circu- 

 lation, the main seat of infection being, apparently, in the spleen, 

 bone marrow, and other internal organs. Infection with this 

 organism is associated with fevers varying greatly in their mani- 

 festations. There may be quotidian or tertian intermittent fever, 

 or, more commonly, more or less continuous fever with irregular 

 remissions. The individual paroxysms last, on an average, about 

 twenty hours. The irregularities in temperature depend, prob- 

 ably, upon variations in the length of the cycle of development 

 of the parasite, or upon infection with multiple groups of or- 

 ganisms. 



" We have not been able to separate two distinct varieties of 

 the sestivo-autumnal parasite, though we feel that more investi- 

 gation is needed upon the subject. 



