Variation in Size of Trypanosoma Brucei. 



3i7 



ceipt, it was suspended in sterile physiological saline and injected 

 subcutaneously into a white rat. In order that some carefully 

 collected data might be acquired concerning possible variations 

 in the size of the micro-organism in the rat and in the guinea pig, 

 blood from this animal very shortly after death was injected into 

 a guinea pig. Heart blood from this guinea pig at the time of its 

 autopsy in turn was injected into another guinea pig and also into 

 a white rat. By this method the host altered from time to time. 

 The series of animals included four rats and four guinea pigs, all 

 of which showed no parasites before the time of use. Numerous 

 slide preparations were made from heart blood as soon after death 

 as possible, within an hour or two at most. These were stained 

 with Wright's stain made up according to the usual formula but 

 diluted with one additional equal part of methyl alcohol. Meas- 

 urements were then made by means of a properly calibrated series 

 of lenses and with a filar micrometer. Slides made from each 

 animal were included. By this means were examined 100 in- 

 dividuals from the guinea pigs and 90 from the rats. All trypano- 

 somes measured were in the fully developed stage with typical 

 morphology*. 



As a result it is found that the average size of Trypanosoma 

 brucei in guinea pigs is 18.46 X 3.16 micra while in white rats it is 

 13.25 X 2.23 micra. The application of statistical methods 

 shows that these two series are comparable since deviations for 

 guinea pig trypanosomes are — length 13^68 and width 4.27 while 

 for white rats they are — length 14.27 and width 3.59. Coefficients 

 of dispersion are: guinea pigs — lengths 0.13 and breadth 0.23; for 

 white rats they are determined to be — length 0.18 and breadth 

 0.27. This variation in the two hosts was apparent throughout 

 the period of active infection. 



We find therefore that Trypanosoma brucei does vary in size 

 according to the host infected and that it is markedly larger in the 

 guinea pig than in the white rat. These findings are comparable 

 to those of Hegner 5 with Trypanosoma diemyctyli in salamanders. 



5 Hegner, Jour. Parasit., 1921, vii, 105. 



