532 



Miss M. Robertson. Polymorphism of [July 5, 



considerably, and it is this variability of the time factor, coupled with the 

 striking appearance of the individuals at either end of the scale, that has led 

 to the belief that the species is really dimorphic. Such figures as 6-8 and 

 1-3, showing respectively short and long forms, have fostered this idea, and 

 seem further to have suggested that the difference is an expression of sex. 

 Neither of these hypotheses has, however, been sufficiently tested. 



If one infection is carefully followed through a typical revolution of the 



Camera drawings, x 2000. 



Figs. 1 — 3, long slender types. Figs. 4 — 5, typical early division stages. Figs. 6—8, 

 short forms. Figs. 9 — 11, intermediate forms. Figs. 12 — 13, rare individuals of 

 intermediate type in division. 



endogenous cycle, the following conditions are found to obtain. It is 

 convenient to choose the period immediately after a marked drop in the 

 numbers, as the starting point. At such a time there are very few trypano- 

 somes present in the peripheral blood, and they are short types.* As a matter 

 of fact, the shortest trypanosomes of the cycle are to be found at this period. 



* See Tables 18 and 9. The tables referred to are not reproduced here, but are 

 reserved for publication in a forthcoming Eeport of the Sleeping Sickness Commission. 



