52 



. 

 Chapter V 



THE MALARIAL PARASITE 

 LIFE HISTORY 



The Protozoa are divided into several classes, one 

 of which is the Sporozoa. 



This class comprises several orders, the most closely 

 allied of which are the Gregarinida (e.g., Monocystis 

 agilis in the seminal vesicles of the earth worm), the 

 Coccidiidea (e.g., Coccidium oviforme in the rabbit's 

 liver) and the Haemosporidia (which include the 

 malarial parasites of man, birds, etc.). There is a close 

 relationship between the Coccidiidea and the Haemos- 

 poridia (malaria parasites), the developmental cycles 

 of the two being almost identical. The develop- 

 mental cycle in the blood (the febrile cycle) of the 

 malaria parasites was first demonstrated by Golgi, the 

 further cycle in the mosquito by Ross. The cycle 

 of Golgi is the asexual cycle, producing auto-infection 

 of the patient ; the cycle of Ross is the sexual cycle, 

 producing a new infection in a healthy subject. 



The sexual cycle, it has been thought, commences 

 in the blood when the conditions are unfavourable 

 for the continuance of the asexual cycle, and, in fact, 

 has been taken as a sign that the patient has already 

 developed immunity against the fever-producing 

 young parasites (spores). Thus it is well known that 

 in malignant tertian the sexual forms, gametes or 

 crescents, first appear about a week to ten days after 



