15 
in thickness from 5 to 15 micra were made from paraffin-embedded 
tissue. The stains used for sections were Weigert’s iron hematoxylm, 
Delafield’s hematoxylin, and Giemsa’s solution for Romanowsky 
staining. Smears from blood and the various organs were prepared, 
both dr}^ and fixed in alcohol, formol alcohol, and methyl alcohol. 
Giemsa’s and Wright’s stains were found the most satisfactory for 
blood smears. 
In dravdng blood from living rats some difficulty is usually expe- 
rienced. If a portion of the tail (about 1^ inches) is removed, 
sufficient blood for smears is readily obtained. If the blood exami- 
nation is to be repeated daily, a slight manipulation causes the 
granulation tissue formed upon the stump to bleed freely. The 
increased number of leucocytes on account of the slight inflammatory 
reaction from the wound does not interfere with the detection of the 
parasite. Obviously blood obtained in this manner could not be used 
for differential or total counts of the wliite blood cells, in whichinstance 
it is necessary to remove another small piece from the extremity. 
In handling the rats a pair of long curved surgical dressing forceps, 
with wliich the animal is grasped by the loose skin at the back of the 
neck, are very convenient. 
Hepatozoox peexiciosum IX THE Blood of White Rats. 
Wlien stained smears made from the blood of infected rats are 
examined vdth the microscope, large oval nucleated bodies are seen 
embedded in the protoplasm of leucocytes. The wffite cells affected 
are almost invariably large mononuclear hunphoc^des, seldom transi- 
tional leucocytes, and very rarelj” polymorphonuclear leucocytes. 
The mononuclear and transitional cells of the rat’s blood resemble 
very closeh^ cells of the same type in human blood. The nuclei stain 
strongly with basic stains, and the protoplasm is free of basic staining 
granules. The nuclei of the former variety are almost alwa^^s excen- 
trically located in the cell protoplasm, and the parasite, when present, 
is usually situated beside the nucleus, where the protoplasm is most 
abundant. In transitional cells the parasite is often wedged in the 
angle formed by the bending of the nucleus. The wliite cells which 
contain parasites appear to suffer in no way by reason of their pres- 
ence. Evidence of degenerative or other changes is lacking. 
A marked increase in the number of leucocytes, especially of the 
large mononuclear variety, is invariably observed when parasites are 
present. Tliis increase varies in direct proportion to the number of 
parasites in the blood. The blood in severe infections, shortly before 
death, strongly suggests that seen in human lymphatic leukemia, 
both in the fresh and stained condition. Xucleated red cells, which 
are present in small numbers in normal rat’s blood, are often greatly 
