926 Transactions of the Society. 



can turn completely round with lightning rapidity, so that the 

 flagellurn, at one moment lashing in one direction, is suddenly 

 observed working in the opposite direction. Then suddenly the 

 organism makes progression, and it can he distinctly seen to move 

 in the direction of the flagellum, the flagellum threading its way 

 "between the corpuscles and drawing the rest of the organism after 

 it. Currents set up by evaporation may undoubtedly here and 

 there produce the appearance of the organism " wriggling along " 

 with its flagellum posterior, but I am convinced in my own mind, 

 after hours of patient observation, that in the normal mode of 

 progression, the flagellum acts as a tractellum and not as a 

 pulsellurn. By treating cover-glass preparations with osmic acid 

 the appearances obtained are very similar to what is shown in 

 Lewis's photographs, so that I have no doubt, in spite of our 

 descriptions not completely according, that they are one and the 

 same organism. A great likeness to the organisms described by 

 Mitrophanow, and to the Surra parasite described in the earlier 

 part of this paper, at once occurred to my mind, and when I 

 had stained the rat parasites the closest examination confirmed 

 my belief that they were morphologically identical with the 

 stained parasites of Surra. 



I passed the cover-glasses with a thin layer of blood three 

 times through the flame of a Bunsen burner in the way commonly 

 employed for examining micro-organisms, and stained them with an 

 aqueous solution of fuchsin, methyl-violet, and Bismarck brown. 

 I have also stained them with aurantia, nigrosin, and other anilin 

 dyes. The following method will however be found most instructive. 

 Use freshly prepared saturated solution of fuchsin or methyl-violet 

 in absolute alcohol, and put a drop with a pipette on the centre of 

 the preparation ; do not disturb the drop-form for a few moments ; 

 then, before the alcohol has evaporated, wash off the excess of stain. 

 It will be found that where the drop rested the organisms will be 

 very deeply stained, while in the surrounding area the colour will 

 vary in intensity. By the effect of the different degrees of stain- 

 ing much may be learnt (fig. 199). In one organism the body and 

 entire membrane will be equally stained ; in another the margin 

 of the membrane only. In some the posterior stiff filament is 

 stained and at its base a darkly stained speck is very striking, 

 and in other cases again the posterior filament is only faintly 

 tinged, or an unstained spot occurs near its base. 



The morphological identity of the rat and Surra parasites 

 is thus established, and both seem morphologically identical 

 with the organism of Mitrophanow. This leads me to speak of 

 the classification of these organisms, for if we follow Mitrophanow, 

 we must obviously enlarge his genus of Htematomonas ; I venture, 

 however, to disagree with Mitrophanow in the advisability of 



