22 
PROPHYLAXIS OF MALARIA. 
In describing the malaria plasmodia two distinct life cycles must 
be considered—first, the human or asexual cycle, called schizogony , 
occurring in man; and second, the mosquito or sexual cycle, called 
sporogony , occurring in the infected mosquito. In each of these 
cycles of development the morphology of the parasites varies greatly 
and should be familiar to everyone engaged in the prophylaxis of the 
malarial fevers. 
In the following descriptions the morphology of the various spe¬ 
cies of human plasmodia will be first given as observed in living 
preparations and then as observed in stained preparations. The 
forms pertaining to the human cycle of development will first be 
described and then the forms concerned in the mosquito cycle. 
Morphology of Plasmodium vivax (the tertian parasite) ( Schi¬ 
zogony or human cycle. —As is well known this species of malaria 
plasmodium completes its cycle of development in the blood of man 
in 48 hours and produces the well-known type of malarial fever 
associated with a chill and fever occurring every other day. 
The parasite is first observed, in unstained preparations, within 
or upon the red blood corpuscle as a small, nonmotile, hyaline ring 
or disk, the trophozoite , measuring about 2 microns in diameter; its 
outline is very indistinct, and it is often overlooked owing to lack 
of amoeboid movement and the delicate veil-like consistency of its 
cytoplasm. As it grows older, becoming the schizont , it develops 
marked amoeboid movement, but is still indistinct in outline until 
pigment is developed at the end of from six to eight hours. The 
pigment is reddish brown in color and arranged irregularly through¬ 
out the cytoplasm in the form of very fine granules. As development 
proceeds the pigment becomes motile, due apparently to currents 
within the cytoplasm of the parasite, while the amoeboid motion of 
the plasmodium becomes less pronounced. As growth proceeds the 
pigment increases gradually in amount and remains active until 
just before sporulation when it becomes collected in large masses or 
a single large irregular mass near the center of the parasite. 
At the end of 24 hours the plasmodium fills more than half of the 
infected red corpuscle, contains much actively motile pigment, and 
varies greatly in shape due to the marked amoeboid activity of the 
organism. The infected red cell is considerably larger than normal 
and lighter green in color. At the end of 36 hours the plasmodium 
has attained its greatest size and practically fills the infected cor¬ 
puscle. Amoeboid motion is sluggish, but the pigment, which has 
still further increased in amount, is very actively motile and is dis¬ 
tributed in the form of fine granules throughout the cytoplasm. The 
cytoplasm of the plasmodium is colorless, but the organism is sharply 
outlined. The infected red corpuscle is almost twice the size of the 
normal corpuscles surrounding it. At the end of 48 hours sporula- 
