138 TRYPANOSOMIASES OF RHODESIA. 



free flagelluni became less nnnnerous, while other forms of all 

 graduation from the long form to tlie " tadpole " type made their 

 appearance. 



Coincidently with the shortening and disappearance of the 

 free flagellum and the gradual rounding of the posterior end, 

 a shrinking of the undulating membrane, which became almost 

 inappreciable in the tadpole form, was noted. The gradations 

 were not acute, 'but one type merged into another, so that it 

 was impossible to determine where the long forms ceased and 

 the non-flagellated types 'began. 



The observation further gave rise to a theory which I ad- 

 vanced at the time, and which recent experiences of other workers 

 seem to support, namely, that such circumstances as the jiro- 

 duction of anti-bodies by the host, or the unsuitability of the 

 uTedium for the existence of the parasite, gave rise to the smaller 

 forms which may be regarded as types de resistance. T was 

 perhaps too bold when I advanced the suggestion that the 

 numerous varieties of animal trypanosomiases met with in the 

 continent of Africa may have had a common origin, their sub- 

 sequent minor points of difference having been brought about by 

 natural conditions of passage, transmission and environment. 

 This certainly cannot be disproved, for such conditions have not 

 and cannot be duplicated in the laboratory, and I maintain that 

 the results obtained in laboratories far removed from a supply 

 of natural virus in natural conditions are entirely artificial, and 

 that the parasites so studied adapt themselves to their new sur- 

 roundings and assume unnatural characters. 



Bagshawe, in the Sleeping Sickness Bulletin No. 18, records 

 this hypothesis and advances the experience of Doflein in sup- 

 port. This worker draws attention to the influence of age, food 

 and other factors upon the morphology of trypanosomes, and 

 instances the change in size and form when 7V. bnicei is trans- 

 mitted from rat to hedgehog. He says : 



" the di'iiiensions of the creature, its mobility, the size of the nucleus 

 and blepharoplast. and above all the relative position of these — all these 

 characters are not only labile in the natural state, but can be intluenced 

 by animal passage and artificial culture-" 



He hints at the possibility of the conversion of one apparent 

 species into another. \A^endelstadt and Fellmer showed by ex- 

 periment 'how Tr. brucei in the blood of adders and tortoises 

 developed forms much smaller than the normal and how that 

 when the strain was returned to rats ( i.e., highly susceptible 

 hosts), very large trypanosomes made their appearance. 



Having advanced this hypothesis with some temerity, it was 

 with great satisfaction that I found so great an authority as 

 Bruce adopting a scale of measurements on a percental basis 

 expressed in the forms of charts or curves, giving the relative 

 prevalence of various types. These charts show a remarkable 

 overlapping or resemblance between various species considered 

 distinct. By this system it was shown that the variety of Tr. 

 diuiorphon met with by observers in Khartoum closely resembled 



