20 
motion. The merozoites move slowly about, gliding over one another, 
like a mass of worms. Often such a cyst is seen to rupture and the 
merozoites escape. In this event they move about as free vermi- 
cides, benchng and twisting and ghding about exactly as will be 
described later in the case of vermicides formed from sporozoites, 
from which they can not be chstingidshed. Some of these vemncules 
enter the hver capillaries and later the circulating blood; others enter 
fresh liver cells and repeat the process of midtiphcation. 
In stained smears made from the hver the- various stages in the 
transformation of the free vermicide into the encysted trophozoite 
are readily traced (pi. ii). In the former the nucleus is composed of 
large chromatin granules and the parasite is slender and elongated. 
It then becomes contracted in length and oval in shape; -still later the 
nucleus is disposed in the characteristic parallel skein arrangement, 
and finally a cyst develops, the parasite being engidfed by a large 
mononuclear lymphocyte. Xo evidence of sexual dimorphism of 
the scliizonts has been noted. The merozoites, when released from 
the cysts, are fuUy developed and do not subsequently increase in 
size in the blood. The large mononuclear leucocytes are foimd in 
in unusual numbers in the hver, in the sinuses of the lymphatic 
glands, the thymus, spleen, and bone marrow. 
There seems to be little doubt that the vermicides, wliich are taken 
in by leucocytes in the liver and elsewhere and become encapsulated 
trophozoites, undergo no further development in the rat. Those ver- 
nncules ivliich escape the phagocytic action of these cells and enter 
other liver cells repeat the process of schizogony. The majority per- 
haps are carried into the peripheral circulation in the leucocytes. 
The liver cysts and merozoites are almost exactly duplicated in size 
and appearance by the sporocysts and sporozoites in the body of the 
intermediate host, to be described later. Encysted trophozoites are 
especially abundant in the spleen, lungs, kidneys, and brain, in the 
blood vessels, and lymph spaces. 
CLINICAL SYMPTOMS IN WHITE RATS. 
When the infection is slight, the rat often presents no evidence of 
disease. For a month or so the blood may show only a few para- 
sites encysted in the leucocytes. This t}q)e of the disease is more 
common in old rats. 
Frequently the disease begins gradually, vdth a few parasites in the 
blood. With the gTadual increase in the amoimt of infection the 
animal becomes more and more anemic. It may continue in tliis 
state for two or three weeks and then gradually recover, or death 
may occur. Other animals, especially those experimentally infected, 
may die tliree or four days after the appearance of parasites in the 
