17 
always the one directed forward when in motion. The posterior 
extremity is narrower, rounded, and nearer the nucleus. The move- 
ments, size, and appearance of the vermicules are identical ^vith 
those of vermicules formed from sporozoites, which will be described 
later in detail. 
PARASITES STAINED. 
In blood smears stained by Giemsa’s or Wright’s stain the parasites 
appear as elongated oval bodies, broader and shorter than in the fresh 
blood, measuring on the average 12 by 6 micra. The nucleus stains 
almost the same color as the nucleus of the leucoc}^te in which it ap- 
pears. The protoplasm of the parasite stains pale blue (more strongly 
at the periphery ), is uniform in character, and is free of granules. The 
nucleus usually occupies the middle third of the parasite; occasion- 
ally it is located at the extremity. In outline the common form is 
somewhat quadrilateral with rounded corners or is irregularly oval. 
Instead of being made up of chromatin granules the nucleus is com- 
posed of skeins or bands of clrromatin, often arranged in a more or 
less parallel fashion at right angles to the parasite. It is probable 
that the nucleus is quite thin and flat, since parasites are frequently 
seen in which the chromatin is arranged in a single narrow band 
near and parallel to one side. Surrounding each parasite and separat- 
ing it from the protoplasm of the leucocyte is a delicate cyst wall, 
which appears usually as a clear, unstained, narrow area of even 
thickness. The superficial layer of protoplasm of the parasite 
seems condensed. That the cyst is an integral part of the latter 
and not of the leucocyte is shown by the fact that free encysted 
forms are occasionially seen. 
The behavior of the parasites toward stains is an additional evi- 
dence of the presence of a cyst wall. When less powerful stains are 
employed than those mentioned the parasite stains vdth great 
difficulty, although the leucocytes are strongly stamed. In faintly 
stained specimens the parasites appear as colorless, refractile bodies, 
the interior being unstained. 
It is noteworthy that in H. perniciosum, as in other hsemogre- 
garines of mammals, the forms met with in the circulation — the tro- 
phozoites — are approximately equal in size. Moreover, the dimen- 
sions do not vary greatly in different animals or in the same animal 
at different times. This peculiarity is explained, as will be shown 
later, by the fact that the parasites are discharged only when fully 
grovTL into the circulating blood. 
In stained specimens the free vermicules are slender, curved or 
straight, with blue staining protoplasm, devoid of granules and 
without a capsule. The nucleus is formed of several rounded chro- 
matic bodies (pi. ii). One extremity is often pointed, and the 
50519— Bull. 46—08 ^2 
