112 
A Study of Trypanosome Strains 
from the "fly-country" were in one strain (I) fed on a monkey and in the case of 
four other strains (II to IV) fed on dogs. From these animals thus infected others 
were inoculated, but in each case only the trypanosomes from a single rat were 
used for purposes of measurement and comparison. The following table gives the 
frequency distributions of the five strains, and chiefly on the basis of these 
distributions, Sir David Bruce and his colleagues conclude that: 
" The five wild Glossina morsitans strains resemble each other closely, and all 
belong to the same species of trypanosome." (p. 421.) 
Wild G. morsitans Strains*'. 
Microns 
15 
10 
17 
IS 
n> 
20 
21 
2^ 
22 
24 
'2-j 
20 
27 28 j 29 
20 
31 
32 
33 
34 
35 
Totals 
Strain I 
3 
11 
25 
56 
62 
75 
53 
31 
28 
44 
16 
23 I 26 
22 
12 
6 
4 
I 
2 
500 
„ 11 
] 
4 
20 
43 
67 
44 
48 
34 
42 
35 
33 43 
28 
23 
19 
13 
1 
500 
„ III 
19 
72 
84 
85 
44 
24 
40 
33 
27 
18 
21 
12 1 11 
3 
4 
3 
500 
„ IV 
1 
5 
37 
60 
71 
54 
34 
25 
17 
13 
15 
19 
34 1 30 
31 
30 
8 
14 
1 
1 
500 
„ V 
6 
4 
27 
57 
94 
49 
37 
22 
14 
13 
11 
19 
25 ] 23 
29 
27 
18 
13 
7 
3 
2 
500 
Sum 
t 
31 
148 
230 
326 
252 
237 
184 
143 
115 
130 
110 
127 i 133 
113 
96 
54 
44 
11 
7 
2 
2500 
Investigating the statistical measure of resemblance in the usual way we have 
the following series of results : 
81-88, 
Strains I and II : 
Strains I and III : 
Strains I and IV : 
Strains I and V : 
Stiains II and III : 
Strains II and IV : 
Strains II and V : 
Strains III and IV 
Strains III and V : 
Strains IV and V : 
T 
X 
X 
X 
F< -000,000,1, 
: 139-71, P < -000,000,01, 
: 10015, P< -000,000,1, 
: 115-77, P < -000,000,1, 
328-12, P< -000,000,01, 
184-88, P < -000,000,01, 
208-79, P < -000,000,01, 
122-79, P < -000,000,1, 
147-20, P < -000,000,1, 
23-90, P = -2470. 
Statistically therefore there is not the faintest resemblance whatever between 
any pair of these strains except the IV and V. These strains are for practical 
purposes interchangeable. In one out of every four trials two pairs of samples of 
500 from the same trypanosome population would give results more divergent than 
those observed. But what is the source of this resemblance ? Why are these two 
strains alike and all the others widely divergent? There is nothing whatever in 
the paper to accouat for this agreement, and it is the more remarkable because 
Strains IV and V are to the statistician the most compound looking of all the 
strains. But some uniformity of origin or treatment has caused the two com- 
ponents to appear in like proportions, and at the back of this resemblance there is 
some vital point, if we could follow it up. Were the two dogs bitten by the same 
* i?. ,S'. Proc. Vol. 86, B, p. 409 et seq. 
