40 
Post-moriem . — Lesions as in Xo. 1. 
Bat Xo. o. — Few encysted parasites on twenty-fifth day. but 
gradual increase up to fiftieth day. Leucocytes 2S.000. 37 per cent 
large mononuclears. In counting 200 leucocytes 28 encysted forms 
observed : none free. Animal appears healthy : shght anemia. 
Bat Xo. 6. — Few free and encysted parasites on nineteenth day. 
On twenty-fifth day greatly increased in number, both free and en- 
cysted: moderate anemia. On fiftieth day animal alive, but seems 
sick and is quite anemic. Leucocytes 98.000, 62 per cent large 
mononuclears: many nucleated reds. In counting 200 leucocytes 
231 parasites observed: 157 free. 
Bat Xo. 7. — Infection appeared twenty-seventh day; death thirty- 
first day: great anemia. On twenty-sixth day leucocytes 91.000. 
59 per cent large mononuclears. In counting 200 leucocytes 101 
parasites observed, mostly encysted. 
Autopsy. — Spleen 6 by 1 by 0.4 cm. Other lesions as in Xo. 1, 
except punctate hemorrhages absent in lungs. 
Bat Xo. 8. — Free vermicules only in small numbers on seventeenth 
day : encysted forms numerous on twenty-fifth day : death thirty- 
sixth day. Leucocytes 126.000. large mononuclears 78 per cent on 
thirty-fifth day. In counting 200 leucocytes 83 parasites, mostly 
encysted, were seen. 
Autopsy. — Lesions as in Xo. 1, except slightly smaller size of spleen. 
Bat Xo. 9 — Control. — Examined every five days up to fiftieth day. 
Xo parasites found. Leucocytes 10.600, few nucleated reds. 
Bat Xo. 10 — Control. — Xo parasites up to fiftieth day. Leuco- 
cytes 5.800. 
Control animals were repeatedly examined and found free of mites. 
INFECTION IN WILD RATS. 
In attempting to infect wild rats {Mus rattus) with H. perniciosurn 
an obstacle was encoimtered. due to the difficulty of handling them 
and of keeping them healthy in captivity. 
In the first experiment five large rats, averaging 250 grams in 
weight, were used. These rats had just been captured in a wire trap. 
They were placed in separate glass jars, to which infected mites had 
been added. Unfommately all the rats died within a week from self- 
starvation and the efi'ects of confinement. 
For a second experiment six yoimg wild rats, apparently of the 
same age and averaging about 100 grams in weight, were obtained. 
These were placed in a large ^vire cage, which in turn was placed in a 
large wooden cage containing infected mites. 
Results: One rat died on the thirty-third day and another on the 
thirty-ninth day. Examination of the blood and organs showed 
