16 
increased in numbers. A series of actual and differential leucocyte 
counts of the blood of rats, with infections of Tar;\dng severity, is 
given below. 
Rat 
Xo. 1 
Large 
lympho- 
c;hes con- 
taining 
parasites. 
X umber 
of para- 
sites free. 
Total white 
blood cells. 
Large 
mononu- 
clears. 
1 
! 
Transi- 
tional. 1 
1 1 
Polymor- 
phonu- 
clears. 
f 
Eosino- 
philes. 
Small 
mononu- 
clears. 
1 
Per cent. 
72. 
2 
36,000 
Per cent. 
62. 
Per cent. 
6.2 
Per cent. 
20.9 
Per cent. 
1.1 
Per cent. 
! 9.8 
2 
16 
4 
32,600 
48 
5.5 
31. 1 
2. 1 
8.3 
3 
•53. 5 
6 
102,000 
65. 1 
9.6 
18.3 
.8 
7. 2 
4 
30 
0 
16,000 
51.3 
4 5 
31.2 
.6 
11 4 
5 
82.5 
6 
128, 000 
78.7 
6. 5 
11.6 
.3 
2.9 
6 
39 
0 
28, 500 
4.5.8 
6 
39.6 
. 5 
8. 1 
7 
48 
1 
64, 000 
.50.1 
8.6 
35. 5 
1.8 
4 
8 
2 
0 
12, 600 
30.2 
8.5 
51 
2 
8.3 
9 
12 
0 
10,800 
3.5.6 
10.5 
48 
1. 5 
4 4 
10 
20.5 
0 
15,200 
30.5 
50.7 
1.6 
10.2 
A number of red blood cell counts made upon the blood of heavily 
infected rats gave from 1,900,000 to 3,200,000 per cubic millimeter. 
Hemoglobin, vdth the Tallquist scale, from 20 to 60 per cent. 
PARASITES IX FRESH BLOOD. 
When a drop of blood is spread out thinly between cover slip and 
slide the parasites are readily made out in the leucocytes. They 
appear as large rod-shaped bodies with rounded extremities and are 
slightly more refractile to light than the leucocytes. Xo nucleus 
can be detected. In the fresh condition the parasite appears longer 
and more slender than when stained. It is often longer than the 
leucocyte in which it is contained, the protoplasm of the latter 
appearing to be stretched somewhat in order to encompass the 
parasite. 
The first studies made upon H. perniciosum in the blood were 
limited to material obtained from naturally infected rats, in all of 
which the infection had existed for some time before the discovery 
of the microorganism. In the blood of these rats nearly all the para- 
sites were in leucocytes, and very few were observed free. In rats 
artificially infected, and m which daily blood examinations were made 
from the beginning, conditions were found to be somewhat different at 
the inception of the disease. 
The first parasites observed in recently infected animals were free 
in the blood plasma, few in number, and actively motile. Later, 
the common encysted forms appeared and the motile forms — :the 
‘ Awmicules’’ — disappeared. In a few rats, vermicides were found 
during the course of the disease and especially just before death. 
The vermicides, as observed, are slender bodies 15 to 16 micra m 
length, with clear delicately striated nongranular protoplasm, some- 
what refractile to light. The anterior extremity, bluntly pointed, is 
