Karl Pearson 
107 
(e) If we turn to the T. pecorum strain as actually found in the tsetse Hy, we 
see that Sir David Bruce and his colleagues deal with these trypanosonies passed 
through a variety of animals, of which only goat and dog sujjply sufificient numbers 
for any even approximately accurate treatment. The data are as follows*: 
Microns. 
9 
10 
11 
12 
13 
U 
15 
16 
17 
IS 
Totals 
Wild G. morsitans strain : Goat 
1 
3 
12 
21 
55 
60 
32 
12 
4 
200 
„ „ Dog 
3 
14 
34 
41 
40 
19 
9 
160 
Wild G. morsitans strain : Rat 
1 
3 
22 
28 
19 
6 
1 
80 
For goat and dog we find 19'518, which give P= •0125. The resemblance 
is therefore far less than we have found for goat and dog in other strains, only 
once in 80 trials from homogeneous material would two samples of such divergent 
character arise. Before we comment on this it seems desirable to compare the 
very inadequate rat data. 
For rat and goat we have 
;^== 12-201, P = -1434. 
For rat and dog we have 
;^2 = 11-370, P = -1245. 
Accordingly we see that for this material the rat strain (i) lies between the 
dog and goat strains, and (ii) is definitely interchangeable with dog and with 
goat, while the dog and goat are much more divergent. Now the sparsity here of 
all the data must prevent any dogmatism ; all we can reach is suggestion for 
further investigation. But the following points should be noted*)*. The trypano- 
somes through the goats were obtained from six different goats, infected directly 
from the wild fly ; the trypanosomes from the dogs were obtained from only four 
different sources, namely from a monkey directly infected by the wild fly, from a 
dog directly infected, and from two goats (89 and 125), the former only of which 
is identical with one of the former six goat sources. Lastly, the rats were infected 
from one dog alone, upon which the tsetse flies had directly fed. This dog is not 
identical with one of the dog sources. Now unless we assume that all the strains 
of the trypanosome found in the tsetse fly are identical — which is certainly not in 
accorda.nce with the differences found in the strains of wild game from the " fly- 
country " — it is by no means certain that the trypanosomes obtained from wild 
0. morsitans, through goat, dog and rat as above noted came from anything like 
the same sources. Further, the closer resemblance between rat and dog strains 
* R. S. Proc. Vol. 87, B, p. 11. 
t B- S. Proc, Vol. 87, B, pp. 10, 11, aud 19 to 22, 
14—2 
