330 
Microscopical appearances. 
The perivascular spaces around the blood vessels in the 
substance of the brain were infiltrated with mononuclear leucocytes, 
chiefly lymphocytes. This change is typical of the sleeping 
sickness brain where the infection is due to T. gambicnse. The 
infiltration was not enormous. I have applied a method of counting 
the mononuclears in the perivascular spaces. The sections cut were 
8 /j. in thickness. 
Length of the vessel 
in section in /j. 
Breadth of the vessel 
in section in /a 
Number of the 
mononuclears 
100 
. 
.j 22*8 
34 
68 
68 
48 
100 
... 
. 
68 
72 
100 
... 
too 
56 
100 
... 
. 
100 
5 6 
68 
... 
... 
68 
45 
136 
... 
. 
68 
40 
100 
. 
85 
45 
136 
. 
100 
116 
100 
. 
85 
35 
>36 
. 
100 
118 
100 
85 
95 
100 
. 
85 
68 
100 
. 
85 
55 
100 
... 
. 
85 
40 
100 
... 
. 
85 
40 
100 
... 
. 
85 
40 
'36 
... 
. 
ICX> 
*5° 
68 
... 
. 
68 
40 
100 
... 
. 
34 
5 ° 
100 
Average 102 
34 
72-8 
48 
61 mononuclears 
I hat is in a space of 102 fJ. x 72 /i x 8 /£ there are 61 mononuclear leucocytes. 
