48 
if the mite in question has previouslr sucked blood from a dis- 
eased animal and sufficient time has elapsed for the development of 
sporocysts. the latter, when dissolved in the intestinal juice of the 
ratj set free the sporozoites. These as vermicides penetrate the 
intestinal wall, enter the veins and lymphatics, and reach the liver. 
Here they penetrate the liver cells and imdergo multiplication. 
Some escape into the general circulation. The merozoites when 
fidly developed are set free in the liver capillaries as vermicnles. 
The majority are speedily taken up by the phagocytic large lympho- 
cytes and become encysted: a few may remain as free vermicules. 
The habit of mites to leave the rat dining the day and retinn at 
night affords ample opportimity for a change of hosts if several ani- 
mals are in the same cage. 
As shown by experiment, in rats fed upon infected mites mix ed 
with bread, free vermicules appear in the blood twenty-foin horns 
later and encysted forms after eight or ten days, whereas rats upon 
which live infected mites are placed show infection only after seven- 
teen to twenty-eight days. The explanation of this difference doubt- 
less depends upon how soon after being placed on the rat an infected 
mite is devoured. 
As already mentioned in the description of the parasite in the body 
of the mitej there is no indication, either in preparations of fresh 
mites or in prepared sections, that the sporozoites become free from 
the sporocysts in the body of the mite or that they are transmitted 
by the mouth parts. The sporocysts show considerable tenacity and 
resistance to rupture. Although sometimes encountered in the 
salivary glands, the sporocysts are common in any part of the body 
of the mite. 
Infection through the aliment aiy canal from an intermediary host 
has not previously been described for a protozoan blood parasite. 
The fact that all of those animals, viz. frogs, snakes, lizards, tiu*- 
tles, etc., in which hiemogregarines are so common, are insectivorous 
suggests a possible mode of infection the same as in white rats. 
Leiicocytozoon cams, the sexual cycle of which Christophers has 
described in the dog tick, may possibly be transmitted in the same 
manner as H. perniciosum. 
The limited experiments seem to indicate that infection with the 
latter by inocidation from one animal to another is impossible. 
