192 MOSQUITOES OF NORTH AMERICA 
nomenon is due the fact that blood examinations made just before a fever- 
paroxysm may be negative, the parasite not having yet reached the periphery. In 
the greatest part of the cases there can only be observed annular parasites, gen- 
erally situated close to the margin of the blood-cell. Rarely there can be found 
adults and schizonts in process of division. The proportion of parasitized cor- 
puscles is variable and in acute cases can reach an enormously high number, far 
beyond what is known to occur in the other two species. 
The gametes have a form characteristic of the species. They were the first 
malarial organisms to be observed. In 1843 Klencke found them but it was 
Laveran who, in November of 1880, in Algeria, recognized them as the causative 
agents of malaria, calling them crescentic bodies or half-moon bodies. On 
account of this very characteristic form of the gametes certain authors have 
placed the organism in a genus by itself, under the name Laverania, in spite of 
the fact that this form is transient and changes to a spherical shape when it 
becomes free in the blood-plasm. 
Ziemann described a form of Plasmodium falciparum which he found in 
Africa, founding it on the more pronounced roundness of the crescents and the 
rarity of their appearance in the peripheral blood. This rarity of the crescents 
is, however, everywhere a frequent occurrence with the pernicious parasite and it 
is particularly accentuated during the epidemic months. This variety, as also 
various species indicated by certain investigators, have not been accepted by the 
majority of good workers. Withal it seems nearly certain that still another 
species of Plasmodium exists, characterized by annular forms identical with 
those of P. falciparum, but developing without provoking the acute attacks char- 
acteristic of this species. 
Plasmodium vivax.—This species is responsible for the benign tertian malaria. 
It is the best studied of all the species, being the one used by Schaudinn in his 
famous researches which have thrown so much light on the biology of the 
malarial parasite. Seen fresh the schizont appears endowed with lively move- 
ments. Schizogony takes place in periods of 48 hours, each parasite liberating 
from 12 to 24 merozoits. It is this species which produces the greatest change 
in the blood-corpuscle. After 16 hours it already presents the characteristic 
granulations of Schiiffner. The parasite, 24 hours after having invaded the 
corpuscle, begins to produce an hypertrophy of the blood-cell which becomes more 
accentuated with the growth of the parasite. Parallel with this change the 
granulations of Schiiffner increase in number and the anemia of the corpuscle, 
which begins with its hypertrophy, continues to grow more pronounced. In 
stained preparations these changes can be very distinctly perceived. The 
gametes are spherical. The macrogametes when fully developed are about 1 1/2 
times as large as the normal red blood-cells; the microgametocytes are very 
slightly larger than the corpuscles. 
The human organism can be parasitized at the same time by more than one 
generation of parasites, either of the same species or of different species. These 
evolve independently of each other and therefore also produce separate fever- 
paroxysms. The “ double benign tertian” is an example which can be cited; 
