1912.] The Measurement of Trypanosoma rhodesiense. 233 



because the variation may be due to the cause just stated, namely, the day 

 of infection. 



4. However, giving these sources of error due weight, we think that the 

 fact that there is a general resemblance between the curves representing the 

 measurements of these three trypanosomes (T. gambiense, T. rhodesiense, 

 T. brucci) shows that the method is a trustworthy one. 



5. The measurements of T. rhodesiense are much closer to those of T. brucei 

 than to those of T. gambiense. We do not consider, however, that identity of 

 measurement would necessarily imply identity of species. We still believe 

 that the difference in internal morphology, namely the presence of the 

 posterior nucleus, is sufficient to separate T. rhodesiense both from T. gambiense 

 and T. brucei. 



6. We think, however, that in the future, in order to get as accurate- 

 results as possible, it will be necessary on any particular day to measure 

 larger samples than 20 trypanosomes. How large these samples must be it 

 is, at present, impossible to say, for we have not the requisite data. This is a 

 point we propose shortly to investigate. At present we would suggest that r 

 in order to eliminate unknown possible variations due to the use of different 

 hosts, samples should always be taken from the same animal, and, as we have 

 shown that there are large variations on different days, samples should be 

 taken on every day of the infection. Tame rats would appear to be the most 

 suitable animals, as they are susceptible to the large majority of pathogenic 

 trypanosomes. (See Addendum.) 



Mr. Walter Stott, Honorary Statistician to the Liverpool School of Tropical 

 Medicine, has kindly examined our figures and curves, and is of opinion that, 

 on the whole, the data at present available are insufficient to enable 

 statistical criticism to be applied, as there are no standard curves for 

 comparison. 



We propose therefore shortly to investigate the subject further from the 

 various additional points of view that we have indicated. 



Addendum, April 29, 1912. — Since writing the preceding we have com- 

 pleted a fresh series of measurements of Trypanosoma rhodesiense from a 

 single rat, beginning with the first day of infection, and measuring 

 100 trypanosomes per day during 10 consecutive clays of infection. We 

 have thus obtained measurements of 1000 trypanosomes from the same rat. 

 On representing the results graphically, it was found that the curve 

 resembled that of Chart 2 (for 600 trypanosomes from rats), rising with 

 slight irregularities to a peak at 26 //, (as does the curve of Chart 2), and then 

 falling rapidly to 34 fi. 



VOL. LXXXV. — B. K 



