1913.] 



causing Disease in Man in Nyasaland. 



287 



Chart 1. — Curve representing the Distribution, by Percentages, in respect to Length, of 

 1500 Individuals of the Trypanosome of Strain II, E . 



■09 10 



t 9 

 c a 



" 7 



°" 5 



4- 

 3 



Microns 



13 



14 



15 



16 



'7 



18 



19 



2o 



21 | 22 



23 



2-4 



25 



26 



27 



2S 



29 



30 



31 



32 



33 



34 



35 



36 





38 























































































































































































































































































































































































































































































































































i 



























































































































































i 























































































































































e- 



































3*9 















This curve is made up of measurements from 60 specimens of trypanosomes 

 taken from the goat, 20 from the sheep, 160 from the monkey, 260 from the 

 dog, and 1000 from the rat. 



In a previous paper it was suggested that 1000 trypanosomes taken at 

 random would be a suitable number to plot a curve from, for purposes of 

 comparison. This is done in Chart 2. 



The taking away of 500 rat trypanosomes has changed, to a great extent, 

 the character of the curve. There is no resemblance between this curve 

 and that given on Chart 1 of Strain I, Mkanyanga. If the two strains, 

 I and II, belong to the same species, then little help can be expected 

 from this system of measurement in classifying trypanosomes. 



It has been suggested by Dr. J. W. W. Stephens that the measurements 

 should be made from one animal, and he proposed the tame rat as a 

 suitable species. There seems much to be said in favour of this. Practically, 

 his proposal is that a series of slides should be made with blood taken on 

 10 consecutive days from a single rat, and that 100 trypanosomes should 

 be drawn each day. But it is no light task to draw 1000 trypanosomes 

 at a magnification of 2000, and afterwards to measure them. We have 

 therefore made a compromise and measure 60 trypanosomes on nine con- 

 secutive days, beginning from the day the parasites first appear in the 

 blood. In order to deal with a round number (500) only 20 are measured on 

 the ninth day. 



