SPOROZOA 245 



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. One attack 

 seems to confer immunity to the special form causing it but 

 probably not to the others. 



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 

 parasite existence in the tissues, especially cells, of higher ani- 

 mals. 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 

 excepting the deserts, mountains, and arctic regions, this disease 

 is very widely distributed. 



Three different parasites producing different clinical entities 

 are known. According to the time, frequency, and order of the 



