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232 cleared, or nearly cleared, of spirochætes. If then a drop of liver juice be examined by the dark-field method, it will be found swarming with spirochætes and with highly refractile granules. The source of the latter is soon apparent, for attention will be directed to spirochætes which are not moving in the usual way, but are in a state of violent contortion, or are, so to speak, shaking themselves to and fro. Indeed, I cannot give a more apt comparison than by likening their movements to those of dogs which have been in water and are shaking themselves vigorously to dry their coats. The object of the spirochætes, however, is to rid themselves of the bright, spherical granules which can be seen within them, and which may or may not be aggregations of the so-called chromatin core. These are forced along the periplastic sheath and suddenly discharged, so that they become free in the medium and dance hither and thither as tiny solid, spherical, brilliantly white particles. In process of time the spirochæte loses its activity, becomes difficult to see, and eventually all that is left of it is the limp and lifeless sheath drifting aimlessly in the fluid and liable to be caught up and swept away by some still vigorous parasite. Such a sheath may still retain one or two of the granules which it has been unable to discharge."

Nature of the spirochœte.—— Opinions differ as to the biology of the spirochæte whether it belongs to the bacteria or to the protozoa. Novy and Knapp,* who regard it as a bacterium, point as evidence to (a) the pale zones in the stained long forms as possibly indicating transverse division; (b) the spiral arrangement and very delicate nature of the flagellum, so unlike in these respects that of the flagellata; (c) its not being killed rapidly and disintegrated by the slow addition of water to the blood; (d) its not being provided with an undulating membrane or being attracted, as the trypanosomes are, by air bubbles in microscopic preparations, the trypanosomes in such circumstances arranging themselves around the bubble, their flagella pointing inwards; (e) its uniform staining; (f) absence of nucleus and blepharoplast. In favour of the protozoal nature of the spirochætes are (a) the presence of an undulating membrane but no flagella in certain species, as for example S. plicatilis and S. refringens; (b) the elements constituting a long spiral are all of approximately the same length, which is that of the individual spirochæte; (c) the parasites are not all of the same