104 
A Study of Trypanosome Strains 
dog or ox. This confirms the view obtained for the wild-game strain, that a 
strain taken through the rat as host is incomparable with strains from other 
animals. 
(c) The totals considered for one species of host in (a) and ih) are rather 
small. Larger numbers are forthcoming for the so-called Mzimba strain of 
trypanosomes taken from a donkey at Mzimba. The frequencies are here*: 
Microns. 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
Totals 
Mziinba Straiu, Dog 
„ „ Rat 
3 
2 
8 
14 
17 
41 
56 
91 
69 
79 
67 
56 
47 
53 
27 
38 
22 
39 
10 
22 
12 
19 
7 
16 
4 
15 
4 
9 
4 
2 
2 
2 
1 
2 
360 
500 
We find = 2.5'499 and P = '0619. Thus only about once in 16 trials should 
we get such a degree of divergence as the two samples present, drawing them from 
the same population. This is very far from such a divergence as we have noted 
in the rat and dog for the Mvera cattle strain, or in the case of rat against other 
animals in the wild-game strain, which was extremely large. The only expla- 
nations that occur to me here are : 
(i) In the case of the wild-game strain and the Mvera cattle strain a single 
rat seems to have provided all the trypanosomes, while in the case of the Mzimba 
strain two rats were used ; this might lessen the influence of individuality. 
(ii) In the case of the Mvera cattle strain and the wild-game strain the 
trypanosomes were ultimately taken from a great nuiuber of individuals. In the 
Mvera cattle case we are told that 32 7o of the herd were affected, and we have 
some details of 16 head of cattle and 5 donkeys naturally iufectedf. In the wild- 
game case, the wild game affected were very numerous, covering cases of eland, 
reedbuck, waterbuck, buslibuck, oribi, koodoo, hartebeeste, buffalo and hyaena. 
Now can we start with the hypothesis that all the individual cattle and all the 
individual wild game were each bitten by a fly carrying the same strain of 
trypanosome ? Have we any more right to suppose a priori that one wild- 
game strain of trypanosome and one cattle strain of trypanosome exist, and ask 
whether these two are identical, than to ask whether the strains carried by hyaena 
and hartebeeste are the same ? We have already (p. 93) seen that the strains 
from two hartebeeste are extremely divergent. What right have we a pj'iori 
to classify all wild-game trypanosomes together and call them a wild-game strain ? 
And if two antelopes, whether of the same or of different species, give widely 
different results, wh}^ are the trypanosomes of oxen of the same herd or donkeys 
and oxen from the same neighbourhood to be classed a jwiori as of one species ? 
R. S. Proc. Vol. 87, B, p. 31. 
t R. S. Proc. Vol. 87, B, p. 15. 
