Karl Pisarson 
93 
became infected, to the rat. The frequencies of lengths of the trypanosomes in 
microns were as follows : 
From Rat 
15 
16 
17 
18 
19 
20 
21 
22 
23 
2Jf 
25 
26 
27 
28 
29 
30 
31 
32 
33 
Si 
35 
Totals 
Hartebeeste (1) ... 
1 
12 
53 
80 
92 
53 
46 
45 
28 
25 
21 
10 
19 
6 
6 
2 
1 
500 
Hartebeeste (2) ... 
1 
1 
11 
30 
47 
79 
51 
51 
44 
37 
36 
35 
28 
24 
11 
3 
8 
1 
2 
500 
Oribi 
1 
10 
22 
77 
109 
90 
57 
28 
19 
23 
15 
21 
14 
6 
5 
2 
1 
500 
Waterbuck 
1 
2 
8 
26 
59 
74 
58 
58 
44 
27 
34 
33 
26 
17 
19 
9 
3 
2 
500 
Reedbuck 
5 
30 
57 
90 
81 
53 
27 
17 
16 
18 
23 
18 
25 
18 
« 
2 
2 
1 
500 
Mzimba (Donkey) | 
Strain j' 
2 
14 
41 
91 
79 
56 
53 
38 
39 
22 
19 
16 
15 
9 
2 
2 
1 
500 
I questioned first whether the strains found in the two Hartebeeste were the 
same ; they give 
108-69, and therefore P < 000,000,1. 
In other words not once in 10,000,000 trials would two such divergent samples 
arise if the Hartebeeste strains were samples of the same population. I now 
compare the Waterbuck and the Oribi; these provide %^ = 109'2.5 and P < 000,000,1, 
and again the extraordinary divergence, not the sameness, is the statistical 
feature. The reader may rest assured that equally incompatible results arise 
when we compare the other antelopes. Statistically we are compelled to assert 
either that the trypanosome strains in these different antelopes were different 
species, or that, not only the infected species of antelope, but the individual 
antelope of the same species (as in the case of the two Hartebeeste) immensely 
modifies the strain of trypanosome. In short not the "sameness" of the strains, 
but their great statistical divergence is the fact which impresses itself on the 
biometrician. No biometrician could possibly accept the view of Sir David Bruce 
and his colleagues that* : 
" It is evident from these tables and charts that the various strains of this 
trypanosome, as they occur in wild game are remarkably alike. This is what 
might be expected. Here the trypanosome is at home ; it is leading a natural 
life. It may be supposed to be saved from variation by constantly passing and 
repassing between the antelope and the tsetse fly." 
Our authors, it will be noted, directly appeal for " likeness " of strains to the 
tables and charts. 
With these immense measures of statistical differentiation, we ask : what would 
be the values of and P, if examples of differentiated strains of trypanosomes could 
be found ? If differences of host or treatment can produce these wide divergences, 
how without a preliminary study of the same strain in different hosts and under 
different treatments can we be certain whether these large divergences mean the 
same strain differently treated, or different species of trypanosomes ? 
* R. S. Proc. Vol. 86, B, p. 406. 
