39 
The first experimental attempts to produce the disease in rats were 
conducted with the intention of simulating the natural method of 
infection. Ten healthy white rats about three-fourths grown and 
just received from a dealer were selected. Each rat was placed in a 
separate glass battery jar with wire-gauze top. Carefid examination 
- failed to disclose any skin parasites except a few lice. Two blood 
smears were made each day on two successive days from each rat. 
In every rat the blood was found to be normal. Mites previously 
infected and showing in about 50 per cent ripe sporocysts when 
crushed, were placed upon eight of these rats. From 20 to 50 mites 
were placed upon each rat. Two rats were kept as controls, no 
mites being placed upon them. The rims of the jars containing these 
rats were smeared with vaseline and they were kept in a separate 
part of the laboratory away from the others. The results were as 
follows : 
Rat No. 1 . — .On the nineteenth day first appearance of parasites in 
the blood as encysted forms in lymphocytes; leucocytes increased. 
Twentieth and twenty-first day: Encysted forms more numerous; 
animal shows marked anemia. Twenty-second day: Lymphocytes 
greatly increased; in addition to many encysted parasites, numerous 
free forms. In fresh preparations some of these are actively moving 
vermicules. Twenty-third day: Leucocytes 120,000, 82 per cent 
being large mononuclear leucocytes. In counting 200 leucocytes 
381 parasites were counted. Animal died. 
Post-mortem . — Muscles and skin extremely pale; blood watery; 
spleen greatly enlarged and dark, measuring 6 by 2 by .5 cm. Liver, 
yellow in color; punctate hemorrhages in lungs. 
Bat No. 2 . — Few enc}’sted parasites on twenty-fifth day, gradually 
increasing in number until thirtv-fifth dav. Anemia slight. At that 
time 38,000 leucocytes, large mononuclears 56 per cent. In count- 
ing 200 leucocytes 32 parasites encountered. On fiftieth day infec- 
tion appears to be about the same. 
Bat No. 3 . — Moderate number of free and encysted forms on 
twenty-second day. Infection increased until death on twenty- 
eighth day. Leucocytes, 132,000, large mononuclears 71 per cent. 
In counting 200 leucocytes 165 parasites observed; few free forms. 
Post-mortem .- — Lesions as in rat Xo. 1, except spleen slightly smaller 
and in addition there is enlargement of abdominal and mesenteric 
lymph glands. 
Bat No. Jj .. — Infection first observed on twenty-eighth day; few 
encysted forms; gradually increasing anemia and number of encysted 
forms; death on thirty-eighth day. Leucocytes 110,000 on thirty- 
sixth day; large mononuclears 68 per cent. In counting 200 leuco- 
cytes 96 parasites observed; veiy few free; nucleated red cells 
abundant. 
