1 
18 
vermicule is longer and slenderer than the encysted parasite. The 
latter imqnestionably originates from the verniicrde and all grada- 
tions between the two are observed, especially in smears from the 
liver. 
In the first stage the vermicrde becomes broader and shorter, 
retaining the granular nucleus; next, the latter is changed to the 
bandlike or homogeneous form, either before or after being eu gulfed 
by a phagocytic mononuclear or transitional white ceU : and finally 
a capside is developed. The ultimate fate of the parasites is uncer- 
tain. In rats vdth a mild grade of infection the encysted tropho- 
zoites may be foimd in moderate numbers six to eight weeks or even 
longer after the onset of the disease; yet when the hvers of such 
anhnals are examined no schizonts are foimd. From this it is 
evident that the trophozoites after becoming encysted may continue 
m the circulation, acting merely as foreign bodies, for some tiine 
after their formation. The pathogenic effects appear, as in other 
hsematozoa, to be caused by toxic substances set free dining the 
stage of midtiphcation. 
In addition to the forms described, others are sometimes observed. 
These consist of shght variations from the usual motionless type, the 
trophozoite. Large oval or even spherical parasites are seen, with 
banded nuclei, sometimes fr'ee. more often in leucocytes, and rarely 
showing signs of a cyst wall (pi. ii). Such parasites are common in 
liver smears, but rare in the circulating blood. Xo evidence of 
sexual cUfferentiation of the trophozoites has been observed, unless 
the forms just described be regarded as sexually different from the 
usual type. It seems more probable that these large parasites are 
A^ery young schizonts, Avhich occasionally, escape from the Hver after 
partial development, into the blood stream. 
XONSEXUAL MULTIPLICATION OF H. PERXICIOSUM IN THE RAT. 
It has already been mentioned that the trophozoites foimd in the 
large lymphocytes are practically uniform in size and appearance. 
Xo form is seen v-hich may be construed as yoimg or partly developed. 
The explanation of this lies in the fact that midtiphcation and devel- 
opment into mature parasites takes place in the cells of a single organ, 
the hver. At an early stage of infection, when parasites are numerous 
in the blood, a section of the hver shows many parasites in various 
stages of schizogony. Similar forms have been found in no other 
organ, although carefidly sought for. The trophozoites are especially 
abundant in the spleen, kidney, and brain, but there is no eAudence 
of midtiphcation in these organs. 
In the capiUaries of the hver are many large hmiphocytes contain- 
ing encysted parasites similar to those encountered in the peripheral 
