I 
37 
fourteen days. When examined at the expiration of this period about 
50 per cent showed heavy infection with ripe cysts. When an infected 
mite was crushed between slide and cover slip in a drop of salt solution 
hundreds of sporocysts containing sporozoites were expressed (pi. xv). 
Only rarely were the sporocysts still contained in the large cyst 
(oocyst), the latter being usually ruptured in the process of crushing 
or dissecting. 
With a view of obtaining a clew to the manner of infection of rats 
in nature, a number of experiments were undertaken to determine 
the effect of various substances upon the sporocysts and the sporo- 
zoites. The observations were made partly upon the warm stage of 
the microscope, but largely without its use; the weather at the time 
being extremely warm, additional heat was often found unnecessary. 
1. Action of fresh rat’s blood. — A drop of a healthy rat’s 
blood was mixed on a slide with ripe sporocysts, covered with a 
cover glass, and ringed with vaseline. No change in the sporocysts 
took place nor was any movement of the sporozoites in them observed 
as long as the sporocysts remained intact. On the contrary, when 
the latter were ruptured b}^ pressure on the cover glass and the 
sporozoites set free in the blood, marked changes took place. After 
about fifteen minutes the sporozoites assumed a more elongated form, 
the principal change of shape taking place in the broad extremity. 
This end became more slender and elongated (but still slightly wider 
than the other) and the tip somewhat pointed. The nucleus was 
visible as a spherical body about one-third distant from the smaller 
extremity. The movement earliest observed consisted of a gradual 
bending until the ends were almost touching, then a sudden spring- 
like resumption of the original shape (pi. xvi). Other sporozoites, 
after becoming bent, became slowly straightened, a peristaltic wave 
of contraction beginning anteriorly and a gradually increasing length 
of sporozoite becoming straightened. A longitudinal contraction of 
the entire parasite, which rendered it shorter and broader, was 
followed by slow contraction in a transverse direction, beginning 
anteriorly, this portion becoming longer and thinner as the wave 
passed backward and causing the sporozoite to be projected slowly 
forward. A bending simultaneous with the longitudinal contraction 
often occurred, and in the following transverse contraction straight- 
ening proceeded from before backward, the anterior slender portion 
often making a distinct angle with the clubbed posterior part. 
With high magnifying powers of the microscope and indirect light 
from the condenser, minute striae, some arranged in an oblique trans- 
verse and others in an oblique longitudinal direction, can be made 
out without much difficulty. These striae are caused presumably by 
minute fibrils — the myocyte-fibrillae commonly observed in gregarines, 
which are capable of contraction. 
