1913.] 



causing Disease in Man in Nyasaland. 



289 



This makes a symmetrical curve, which ascends and descends by fairly 

 regular steps, but with little likeness to Charts 1 and 2. 



In an organism low in the scale of nature, such as this, subject to great 

 variation in form, it might be thought that it would not be likely to behave 

 in any two rats in the same way. The following chart shows that this is 

 not so, but that, on the contrary, the same strain of trypanosome planted in 

 two different animals of the same species grows in a remarkably similar way. 



Chart 4. — Curve representing the Distribution, by Percentages, in respect to Length, of 



500 Individuals of the Trypanosome of Strain II, E , taken on nine consecutive 



days from Eat 726. 



Microns 



13 



1 + 



15 



16 17 



18 



; 3 



20 







24 



25 



26 27 



26 



?£>j3ojol 



32j33 



3 + | 3S|36|37 

















































































































































































































































































































































































































































































































I 











































A 











































































































































































































































































































































































































































































6 





























1 









19 

 18 



17 

 16 



IS 

 14 

 <0 13 

 W 12 



id J' 

 -P 10 



C 9 

 W 



(J s 



^7 

 a 6 



5 



It is remarkable how much alike these last two curves are. If curves 

 made in this way from different strains of oue species of trypanosome 

 showed the same degree of similarity, this method would certainly be useful 

 for purposes of classification. But, as we have seen, the curve of Strain II 

 has no resemblance to that of Strain I, and it will be found that each 

 human strain of this species of trypanosome differs, more or less, when 

 subjected to this method of measurement. 



As the occurrence of posterior-nuclear forms has been made the 

 distinguishing character between Trypanosoma brucei, gambiense, and 

 rhodesicnse, it will be of interest to note the percentage of these forms in 

 the various strains. The method used is to count the number of posterior 



