1128 PATHOGENIC PROTOZOA 



reinfections. They are most frequent after quartan, then tertian, 

 and least following asstivo-autumnal. 



The cause of the relapse is still a matter of discussion ; Schaudinn 

 explained it as due to parthenogenesis, the macrogamete changing to 

 a schizont after expelling a part of its nucleus and cytoplasm and so 

 starting a new cycle of asexual parasites. Craig has suggested an 

 intra-corpuscular conjugation as the beginning of a new crop of 

 parasites. It is possible that the old theory, that parasites survive 

 for long periods in the viscera, is correct and that the relapse is 

 brought about by any condition which temporarily reduces the con- 

 valescent's immunity, such as fatigue, etc. H. C. Clark, in Panama, 

 has examined a large series of placentas from apparently healthy 

 women and found that not infrequently they contained plasmodia in 

 large numbers, even in the absence of recent malarial attacks. There 

 was, evidently, sufficient immunity to hold the parasites in check 

 under ordinary circumstances. 



Under ordinary conditions the disease prevails more extensively 

 and in a more severe form among recent arrivals in a district than 

 among the older residents ; while this is no doubt partly due to an 

 acquired immunity, it is not improbable that education in the proper 

 methods of treatment of the acute disease, to prevent relapses; in 

 the avoidance of notoriously dangerous areas, and in the selection 

 for favorable sites for dwelling, and the protection of the individual 

 by screens, are of equal importance in protecting the older residents. 



A specially severe form of malaria has been called "campaign 

 malaria," which develops among troops in endemic areas. In such 

 cases the housing, and food conditions are usually poor, the men 

 are engaged in hard and dangerous work at all hours of the day 

 and night, with the result that they are repeatedly Htten by 

 anophelines, and their blood shows a multiple infection. 



BLACK WATER FEVER 



This condition follows malaria and occurs only in malarial dis- 

 tricts, and by most authorities is believed to be a sequel of the 

 disease, due to some unknown factor. It is characterized by the 

 passage of urine containing hemoglobin, albumin and casts. In 

 color the urine varies from a pale red to a black. Castellani and 

 Chalmers, however, separate it into three forms, symptomatic, toxic 



