THE TRYPANOSOMA BRUCII. 451 



length of time. This method obviates pressure, and the organ- 

 ism may be easily studied with even the highest powers. 

 The Trypanosoma will then be seen to consist of a worm-like 

 body, more or less homogeneous in structure, with at one end a 

 blunt, stiff extremity, and at the other a long, wavy flagellum. 

 With good illumination this flagellum can be seen to be 

 continuous with a wavy membrane which extends along 

 one surface of the long axis of the organism. For some 

 time the Trypanosoma will be seen to be in active 

 motion, which is caused by the rapid lashing movements of 

 the flagellum, by the wavy movements of the undulating 

 membrane, and b}'' the contractions and relaxations of the 

 protoplasmic mass forming the body. In order to arrest 

 this movement a drop of 1 per cent, gelatine solution, or of 

 a weak solution of cherry-gum, should be mixed with the 

 blood, which will so reduce the movement that it will be 

 quite easy to study as much of the organism as can be made 

 out in unstained preparations. In order to see the structnre 

 of the living organism, dark ground illumination, or mono- 

 chromatic light must be used. The former is difficult to 

 use with an immersion lens, but can bo very satisfactorily 

 used with a 2 mm. immersion objective, after the method of 

 Gebhardt.^ We have used spectral monochromatic light 

 (blue), but very good results can also be obtained more 

 easily with Giffoi'd's malachite-green screen. With these 

 methods of illumination the organism appears as a highly 

 refractive body, and near the middle is seen a darker mass 

 — the nucleus ; and near the blunt, stiff end of the body is 

 seen a tiny dark dot, which we will here call the micro- 

 nucleus ; the question of its proper nomenclature will be 

 discussed later. At the same end of the Trypanosoma, in 

 varying relations to the micronucleus, is seen a vacuole. 

 The protoplasm is now seen not to be uniform, but it appears 

 to have an alveolar structure, as described by Biitschli. 

 With regard to the movements of the organisms, the 

 commoner mode of progression would seem to be with the 

 • ' Zeitscliiift fur wissenschaftlicbe Mikrosko[)ie,' Band xv, p. 289. 



