On the Organism found in the Tsetse Fly Disease. 275 



mass of protoplasm forming the body, and by the movements of an 

 undulating membrane which is attached to one surface of the body, 

 and which appears to undulate synchronously with the contractions of 

 the protoplasmic body. This membrane is, excepting at the free edge, 

 very transparent, and can be seen much better in citrated blood which 

 has been thickened by the addition of a small drop of 1 per cent, 

 gelatine solution, when its contour and attachments can be much 

 better made out, owing to the slower rate of vibration effected by the 

 thickened medium. 



The general shape of the Trypanosoma, when rendered quiescent by 

 this means but not killed, is that of a long oval, with one end blunt 

 and the other continued into the flagellum ; the membrane is then seen 

 to be attached to one side of the body ; it begins a little in front of 

 the blunt end of the organism, and is continued at the end into the 

 flagellum. 



But with better illumination, such as a very oblique pencil of rays, 

 or, better still, with monochromatic light (green or blue), the proto- 

 plasm is seen not to be homogeneous. The organism appears then as 

 a highly refractive body, and near the middle, or between it and the 

 flagellate end, is seen a large dark body much more refractive than the 

 rest of the protoplasm; this is the macronucleus. Near the thick, 

 stiff end of the body a tiny still more refractive body (with mono- 

 chromatic light nearly black) is seen, which is the micronucleus. The 

 addition of a drop of 5 per cent, acetic acid makes both of these bodies 

 much more distinct. At the stiff end of the Trypanosoma, in varying 

 relation to the micronucleus, is seen a vacuole. There is no suggestion 

 of a mouth or of any organs, but the protoplasm with the most careful 

 illumination appears not to be uniform, which suggests an alveolar 

 structure, as described by Biitschli. With the ordinary simple stains 

 (hematoxylin, fuchsin, methylene-blue, thionin) the differentiation is 

 not much better than can be observed by careful illumination of living 

 unstained organisms, as these stains are with these, and similar 

 organisms, too diffuse to be of any service. Acting on a method 

 which Ehrlich originated in 1889, and which Eomanowsky modified in 

 1891, and which has still been further elaborated by Ziemann in 1898, 

 we have used a mixture of methylene-blue and erythrosin, which has 

 enabled us to follow the different stages of the Trypanosoma with 

 certainty. This method depends on the fact that when a basic and an 

 acid stain are mixed together in certain proportions, a third neutral 

 body is formed, which has a specific colour reaction with chromatin. 

 By the use of this method we have been able to trace the various 

 stages of the organism in the blood and organs of the affected animals, 

 which is not possible with the ordinary stains, these being useless for 

 many of the forms to be presently described. With this method the 

 macronucleus of the Trypanosoma is stained a clear, transparent, crim- 



