1912.] The Measurement of Trypanosoma rhodesiense. 225 



placed over the drawing of the trypanosome, which is seen through it. When 

 the tracing paper is fixed by slight pressure of the pin placed on the ink line, 

 the tracing paper can be rotated and the most tortuous curves followed with 

 ease. One end of the ink line is placed on one end of the trypanosome. If 

 the axis of the trypanosome curves, for example, at the nucleus, the pin is 

 placed at this point and the paper is now rotated until the ink line coincides 

 with the new direction of the axis. This is done as often as is necessary, 

 and in fact the sharpest curves can be followed in this way, which is 

 impossible by a compass, the points of which are at a fixed distance. Finally 

 the other end of the trypanosome is reached, the pin is placed there and the 

 actual extent of the ink line traversed is measured by the millimetre scale. 

 Further, the method has the advantage that it can equally well be applied to 

 the measurement of any other curved line, for example, the axis of a spirochaete. 



(b) Another objection to the compass method is that, if a start be made at 

 the non-flagellar end of the trypanosome, it is uncertain that the finish will 

 be exactly at the end of the flagellum. If not, there is always a portion of 

 a compass distance which has to be guessed. With the tangent line method 

 this is avoided, and the finish is exactly at the end. 



The measurements could also be made by a self-registering rotameter 

 (" map-measurer "), but we think that it is not quite such a convenient 

 method for accurately following the curve. 



It may be added that all the trypanosomes were outlined by one of us, and 

 measured by the other. 



Measurements and Results. 



The following table gives the distribution, in respect to length, of 

 1000 specimens of T. rhodesiense taken from various hosts, and measured in 

 groups of 20 consecutive trypanosomes, neglecting only dividing forms. 



