causing Disease in Man in Nyasaland. 



129 



Table XX. — Percentages of Posterior-nuclear Forms found among the Short 

 and Stumpy Varieties of the Trypanosome of the Human, Wild-game, 

 Wild Glossina morsitans, and Naturally Infected Dog Strains. 



Date. 



Strain. 



Animal. 



Percentage among short 

 and stumpy forms. 



1912 

 1912 

 1912 

 1912 





Eat 



17 -8 

 26 -2 

 12 -5 

 2 -4 



Wild -game 





Wild 6r. morsitans 





Naturally infected dog 







Comparison of the Morphology of the Naturally Infected Dog Strain 

 with the other Strains of the Trypanosome causing Disease in 

 Man in Nyasaland. 



At the outset it may be stated that it is impossible to separate the 

 Naturally Infected Dog strain from the other strain by microscopical examina- 

 tion. As far as can be made out it is identical in shape, size and position 

 of nucleus and micronucleus, contents of cell, and disposal of the undulating 

 membrane. 



Three plates are given at the end of this paper to illustrate the morphology 

 of this strain, and if they are compared with the plates given of the other 

 strains* this statement will be borne out. 



On the other hand, there are very few posterior-nuclear forms, although 

 in one instance they ran up to 23 per cent., and, as a rule, the thick, blunt- 

 ended type is not so common in this strain as in the others. But for- all 

 practical purposes it must be concluded that the Naturally Infected Dog 

 strain is so similar in appearance to the others that it would be impossible 

 to separate it by morphology alone. 



How this aberrant strain arose in these three chronically infected dogs it 

 is impossible to say. If it had been found anywhere else — in man, game, 

 or fly — the position would have been simplified. But in none of them 

 did anything like the Naturally Infected Dog strain appear. It was thought 

 that perhaps the long sojourn in the blood of the dog had modified and 

 weakened this strain, and attempts were made to prove this, but without 

 success. All the dogs inoculated with the ordinary strains died in a few 

 weeks, and inoculations from those which lingered longest showed no signs 

 of weakening or change of any kind. 



* 'Boy. Soc. Proc.,' B, vol. 87, p. 35 (1913). Ibid., B, vol. 87, p. 493 (1914) 

 " Description of a Strain of Trypanosoma brucei from Zululand." 



