Karl Pearson 103 
Microns. 
9 
10 
1 
11 1 13 
1 
3 ! 14 
3 11 
13 
H 
15 
16 
i7 
Totals 
Mvera Cattle, Goat ... 
1 
1 
22 
27 
26 
30 
19 
21 
13 
8 
1 
100 
100 
We have ■)^- = 5"396 leading to P= "714, or in 71 pairs of samples out of 100 
from a homogeneous population, we should get more divergent results. It follows 
therefore that, as far as these small series of this strain go, goat and dog are 
interchangeable as hosts. 
Let us go a stage further and ask whether ox is interchangeable with goat and 
dog. The following is the frequency distribution for the trypanosomes through 
the ox : 
Microns. 
,9 
10 
11 
13 
13 
u 
15 
16 
17 
18 
Totals 
Mvera Cattle, Ox 
7 
18 
33 
44 
49 
21 
7 
1 
180 
Compared with the goat strain, this gives 
= 9-559 and P = -3888, 
and compared with the dog strain 
X'^ = 9-461 and P = -3973. 
Thus in about two out of five trials from a same population we should get 
pairs of samples differing more than the dog and goat strains do from the ox 
strain. We conclude that while for practical purposes dog, goat and ox strains in 
the Mvera cattle trypanosomes are interchangeable, yet the dog, and goat stiain 
are nearly twice as much alike as the ox strain is to either. Lastly — although it 
is rather a rash proceeding — I compare rat with goat and dog. It is rash because 
only 40 trypanosomes through the rat were measured, and this is wholly inadequate 
for real determination. The frequencies for the lengths are : 
9 
10 
11 
13 
13 
u 
15 
16 
17 
Totals 
Mvera Cattle, Rat ... 
„ „ Dog and Goat 
1 
1 
6 
25 
2 
49 
16 
56 
12 
40 
10 
21 
1 
40 
200 
We find = 21-329 and P = -0064. The small series of rat trypanosomes 
probably accounts for no smaller value of P, but the odds of 155 to 1 are 
sufficient to show that rat series must not be mixed with series from the goat, 
