Karl Pearson 115 
Human Strains. B : From Rat only — (continued). 
Microns. 
AS 
29 
SO 
31 
5.i 
35 
30 
37 
Totals 
Strain I, Mkauyaiiga 
57 
57 
35 
21 
18 
11 
6 
1 
600 
11, E, Rat 728 
12 
15 
6 
1 
500 
II, E, Rat 726 
8 
4 
4 
2 
1 
— 
500 
„ III, Chitiiluka, Rat 952 
41 
48 
28 
43 
27 
23 
10 
4 
5 
1 
1 
500 
„ III, Chituluka, Rat 953 
37 
47 
37 
33 
41 
23 
12 
4 
3 
500 
„ IV, Chipochola, Rat 1337 
31 
14 
13 
2 
— 
500 
„ V, Chibibi, Rat 1660 ... 
33 
25 
11 
6 
1 
500 
Sum 
219 
210 
134 
108 
88 
57 
28 
9 
1 
1 
3600 
This table with its two pairs of rats inoculated from the same strains is 
peculiarly instructive. We can compare II, Rat 726, with 11, Rat 728. 
We find: = 36-195, giving P = -0048. 
This is far from the liigh degree of divergence we have found between the com- 
pound human strains, but it is not satisfactory as a measure of the agreement of 
the same strain in two hosts of the same species. 
Applying the same test to the two Rats 952 and 953 of Strain III we have : 
;)^;2 = 14-715, giving P = -9038. 
This is, of course, quite satisfactory. We should not hesitate to assert identity 
of strains and of treatment in the case of the trypanosomes from these two rats. 
The statistician will feel fairly confident that there is a factor of divergence 
between the trypanosomes of the two rats in Strain II, which does not occur in 
the two rats of Strain III. He will be almost certain that the strain was not 
conveyed through the same steps or at the same stage of the disease to the rats in 
Strain II. Unfortunately dates and processes are not discussed. Sir David Bruce 
and his colleagues say that it is remarkable how much alike these distributions for 
Rats 726 and 728 are, and again for the distributions for Rats 952 and 953 that 
they also closely resemble each other. "It is curious and striking that the same 
strain of trypanosome growing in two different animals should show this remarkable 
similarity*." The interesting point is that the statistician would agree with the 
remarkable similarity in the latter case, but the divergence not the remarkable 
resemblance in the first case would force him to seek for some explanation in 
treatment. It will, I think, be clear from these illustrations that a strain of 
trypanosomes, even if obviously compound, can be taken from a single source and 
after inoculation into two different individuals of the same species be identified 
as same; but to insure this result on every repetition the greatest caution will 
have to be exercised as to identity of process and treatment. 
* B.. S. Proc. Vol. 86, B, pp. 289 aud 293. 
15—2 
