PARASITIC PROTOZOA 359 



vivax, malaria and falciparum, causing respectively the tertian, 

 quartan and remittent types of malarial fever in man. 



The life history of all of these is very similar, the principal 

 difference being in the length of time it takes them to sporulate. 

 Let us begin with the parasite after it has been introduced into 

 the blood and trace its development there. At first it is slender 

 and rod-like in shape. It has some power of movement in the 

 blood-plasma. Very soon it attacks one of the red blood- 

 corpuscles and gradually pierces its way through the wall and 

 into the corpuscle substance; here it becomes more amoeboid 

 and continues to move about, feeding all the time on the 

 corpuscle substance, gradually destroying the whole blood 

 cell. As the parasite feeds and grows there is deposited within 

 its body a blackish or bro\vnish pigment known as melanin. 



During the time that the parasite is feeding and growing it 

 is also giving off waste products, but as the parasite is com- 

 pletely inclosed, in the corpuscle wall these waste products 

 cannot escape until the wall bursts. After about forty hours, 

 if the parasite is vivax, or about sixty-five hours if it is malaria, 

 it becomes immobile, the nucleus divides again and again and 

 the protoplasm collects around these nuclei, forming a number 

 of small cells, or spores, as they are called. In about forty- 

 eight or seventy-two hours, depending on whether the parasite 

 is vivax or malaria, the wall of the corpuscle bursts and all these 

 spores with the black pigment and the waste products that 

 have been stored away within the cell are liberated into the 

 blood-plasma. 



These spores are round or somewhat amoeboid and are carried 

 in the blood-plasma for a short time. Very soon, however, 

 each one attacks a new red corpuscle and the process of 

 feeding, growth and spore-formation continues, taking exactly 

 the same time for development as in the first generation, so that 

 every forty-eight hours in the case of vivax, and every seventy- 

 two hours in the case of malaria, a new lot of these spores and 

 the accompanying waste products are thrown out into the 

 blood. Thus in a very short time many generations of this 

 parasite occur, and thousands or hundreds of thousands of the 

 red blood corpuscles are destroyed, leaving the patient weak 



