.32 
could be conveniently followed with the microscope for an hour or 
more. 
Blood from a rat containing numerous parasites encysted in 
lymphocytes was mixed with the expressed body juices of mutes, 
placed upon a slide, and examined with the microscope. In the 
course of ten to thirty minutes the protoplasm of the lymphocyte 
was partly dissolved and the parasites were set free. 
The encysted parasites, after becoming free from the leucocytes, 
are slender, elongated bodies, rounded at the extremities. They 
show no movement or change of form. After thirty minutes or 
longer the delicate cyst wall surrounding them is ruptured and the 
parasite becomes an actively motile vermicule. The remains of the 
cyst, as a transparent shadow, often continues to be attached to the 
vermicule for some time. 
The same changes may be observed when a mite that has just fed 
upon blood is crushed and the expressed fluid examined. 
Wlien mites starved for forty-eight hours or longer are examined 
six hours after being placed upon heavily infected rats, numerous free 
vermicides are found in the stomach and its diverticula. When these 
mites are crushed under a cover slip in a drop of 0.3 per cent salt 
solution, the vermicules and a considerable number of pol^’-morpho- 
nuclear leucocytes are observed. Other kinds of leucocytes appear 
to be quickly destro}^ed. Not infrequently the remains of the delicate 
cyst which inclosed the parasite is seen attached to some portion 
of the vermicule. In form and appearance the vermicules do not 
differ from those developed from the sporozoites. The movements, 
however, although fairl}^ active at first, become quite sluggish, and 
in mites examined eighteen hours after feeding, motile forms are 
seldom seen. 
The red blood cells disappear very quickly after the ingestion of 
the blood, but hematin crystals, polymorphonuclear leucocytes, and 
free parasites are abundant. The polymorphonuclears are especially 
resistant and appear to remain unchanged after a number of hours in 
the digestive tract of the acariens. The parasites become detached 
from the lymphocytes when these are digested. In mites examined 
twenty-four hours after feeding, the digestive fluid contains single and 
paired vermicules in which movement has ceased. 
The form and arrangement of the paired vermicules is peculiar and 
characteristic. In the earliest stages the 3 ^ are somewhat spindle 
shaped and two extremities are in apposition (pi. xiii, fig. 1 ). This 
constitutes the earliest phase of conjugation or sexual union. A little 
later the vermicules are placed side by side and parallel, the extrem- 
ities even. In appearance they are exactly similar, and hence without 
distinguishing sexual characters. In slightly later stages the adj oining 
