MALARIAL PARASITES 223 



Cultivation. They are cultivated in the manner given for Trep. 

 pallidum by Noguchi, by adding citrated, therefore defibrinated, 

 blood to serum or ascitic-fluid-fresh-tissue-agar. They breed true 

 to type. They remain alive several days under favorable artificial 

 conditions but cannot be cultivated after they have left the body a 

 few hours without being on suitable culture media. 



The periods of fever last from five to seven days, when a crisis 

 occurs. After an apyrexial period the fever recurs. The spiro- 

 chaetae are found in great numbers in every microscopical field. 



In the apyrexial period the spleen becomes engorged and the 

 leucocytes devour the parasites. Monkeys with excised spleens are 

 more susceptible to infection than others. 



Immunity. The blood from rats that have been immunized by 

 repeated injections of blood from spirochetal rats, if injected into 

 other rats, is capable of conferring an immunity on them by causing 

 spirochaetes to disappear from their blood. 



SPOROZOA. 



The most important of this family are the malarial parasites 

 (which belong to the order Haemosporidia), and the Coccidia. 



In general the sporozoa are unicellular organisms that lead a 

 parasitic existence in the tissues, especially cells, of higher animals. 

 They ingest liquid food, have no cilia in the adult stage, and flagella 

 are possessed only by the males. There may be one or more nuclei. 

 Propagation is effected by spores, but budding and division do 

 occur, though rarely. Alternate generation takes place frequently. 



MALARIAL PARASITES. 



Haemosporidia of Man. The most important disease caused 

 in human beings by the haemosporidia is malaria, or ague, and ex- 

 cepting the deserts, mountains, and arctic regions, this disease is 

 very widely distributed. 



