9G A Study of Tri/panosome Strains 
words once in about 50 trials we might expect to get two samples from the same 
population as divergent or more divergent than the distributions found for 
T. brucei and T. rhodesiense. We have in fact in the cases of these two trypano- 
soines reached our first instance of comparative sameness, and the statistics should 
have shown Sir David Bruce and his colleagues that T. brucei and T. rliodesiense 
were relatively the same, and though both differed from the human trypanosome 
of Nyasaland widely, the approach to T. rhodesiense was only slightly closer. 
The accordance — speaking in a relative sense — of T. rhodesiense. and T. brucei 
was asserted by Stephens and Fantham in March, 1912*. In May, 1912, Bruce 
and others, speaking of the T. rhodesiense, term it a distinct species ; in February, 
1913, they say — although without publishing further frequency distributions — 
that "There is some reason for the belief that T. rhodesiense and T. brucei 
(Plimmer and Bradford) are one and the same species," -f- and in a further paper of 
the same month, " Evidence is accumulating than T. rhodesiense and T. brucei 
(Plimmer and Bradford) are identicalj." In May, 1913 {R. S. Proc. Vol. 87, B, 
p. 34), we are told that the Mzimba strain is identical with the wild-game strain 
and that " it has already been concluded that this species is T. brucei vel T. rhode- 
siense." As far as the statistics of the subject go the only really weighty evidence 
for the identity is that of 1912, on which, without statistical analysis, the 
distinction between the two species was asserted. 
(c) We will next consider the possible identification of _T. gambiense with 
T. rhodesiense and with T. brucei. 
The second identification is suggested by Sir D. Bruce and others in the words§ : 
" Whether these slight differences are fundamental or only accidental it is 
impossible at present to say, but enough has been written to show that Trypano- 
soma gambiense and Trypanosoma brucei approach each other very closely in 
shape and size." 
The following table|j provides the data for T. gambiense to be compared with 
the distribution of T. rhodesiense ranging from 12 to 39 in the last table. 
Microns. 
12 
13 
l.'j 
10 
17 
18 
19 
20 
21 
22 
23 
24 
25 1 26 
27 
28 
29 
30 
31 
32 33 
34 
35 
36 
37 
38 
39 
Totals 
1 
9 
21 
56 
79 
114 
122 
110 
85 
85 
61 
47 1 49 
47 
44 
31 
20 
11 
4 4 
1000 
The trypanosomes are from a variety of hosts. 
For the 28 classes we have, 140'27 and P < •000,000,1. The chief point 
therefore is the complete divergence, not the resemblance of the two series. 
" R. S. Proc. Vol. 85, p. 238, 1912. § R. S. Proc. Vol. 84, B, p. 332. 
t R. S. Proc. Vol. 80, B, p. 407. || R. S. Proc. Vol. 84, B, p. 330. 
+ R. S. Proc. Vol. 86, B, p. 302. 
