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516 not required; but in cold weather it is well, until the observer has become by practice familiar with the appearance of the parasite in its passive condition, to warm the slide. This, in the absence of more elaborate apparatus, may be conveniently done by placing the slide on a copper or tin plate with a hole cut in it to allow of the transmission of light. Such a warm stage should be provided with a long arm to the end of which a spirit-lamp is applied, care being taken not to raise the temperature of the slide above blood heat. Search is then made with a half-inch objective. The dysentery amoeba is a clear, faintly greenish-tinted, transparent body, some three to five times the diameter of a red blood-corpuscle. In its vegetative phase it is recognizable by its movements, which closely resemble those of the ordinary fresh- water amœba. The faintly granular endosarc surrounded by the very clear ectosarc is distinguishable. The nucleus may sometimes be detected in the endosarc, as well as one or two non-contractile vacuoles, and, generally, various extraneous bodies such as blood corpuscles, bacteria, and so forth, which the amoeba has included. As the temperature of the slide approaches blood heat the amoebae send out and retract rounded pseudopodia. These when first protruded consist of ectosarc only; but when the clear protrusion of ectosarc has been extended a little way the endosarc is seen suddenly to burst, as it were, and flow into it. If the temperature of the slide be allowed to fall below 75F. the parasite will assume a sharply outlined spherical form and remain quite passive until the slide is again warmed up, when the creeping movement may be resumed. The parasite will keep alive on the slide and exhibit movement for an hour or longer. In certain specimens heat fails to induce movement, the amoeba remaining spherical and passive, being either dead or having become encysted.

There can be no question as to the occurrence of this parasite in certain cases of dysentery, but it is not so easy to determine its exact significance in relation to the disease. It is found not only in the