88 
A Study of Truimnosome Strains 
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cc. Whitechapel ? 's. 
dd. Moorfields ? 's. 
Diagram I his. 
of the same strain. That P = -25 and not, say, -85 may be merely a result of 
random sampling, or it may arise from some difference of period or social class. 
(2) In a long series of papers recently published in the Proceedings of the 
Royal Society, Section B, conclusions are reached as to the identity of various 
strains of trypanosomes. These conclusions are largely based on a comparison of 
graphs of the frequency percentages obtained by measurement of hundreds of 
trypanosomes. 
To some extent mean values are given for the diffei'ent strains, but no argu- 
ments whatever can be based on them, for in no case has the probable error of the 
difference been calculated. Even if it had been calculated, this constant alone 
would not have sufficed to determine the sameness or difference of the strains. 
Further, the pei'centages of various forms in the strains are sometimes given; 
but again no attempt has been made to determine whether the differences of 
these percentages are or are not significant. It seems sufficient here to consider 
the far more valid test of the sameness or diversity of the frequency-distributions 
as a whole. 
I shall divide my investigation into four parts : 
(i) The probability of identity of the strains on the evidence presented in the 
reports of the Commission of tlie Eoyal Society, Nyasaland, 1912. 
(ii) The probability that the host or the animal in which the trypanosome is 
cultivated makes essential differences in the distributions of frequency. 
