The leprous nodes have on section a smooth, white, glistening surface, if they are still sufficiently young. If one examines, microscopically, sections or teased preparations of fresh nodules, one sees little else but cells, with distinct nuclei, usually of the size of a white blood corpuscle, or rather larger. There are also a few larger so-called epithelioid cells, with larger nuclei, and among the cells, fragments of connective tissue and of blood vessels. With a higher power, one sees in the fluid of the preparation small straight rods, which are not destroyed by addition of potash. These are the lepra bacilli, and thus were they first discovered in the year 1871. If one teases out preparations in osmic acid solution, or soaks a nodule in the solution some hours before teasing, the rods are coloured faint brown, and one finds them lying mostly in the cells (_Plate VI, Fig. 1_). If one adds water to a fresh preparation, the bacilli move actively; even in the cells swollen up with water, one sees the bacilli moving; and this led us to regard them as movable, although we at the same time indicated a doubt whether the movement was not simply a molecular one; for the movements were equally vigorous in strong osmic acid solution as in water, and on the addition of glycerine or strong solution of albumen to the preparations, the movements ceased. All later observers, with the exception of Unna, regard the bacilli as motionless. We have no ambition to decide this question, because we know no absolutely trustworthy distinction between molecular movement and independent movement of the bacilli. The older the nodules become, the more large multinuclear cells are found, and in nodules of the skin and cornea one always finds small flat cells with processes, and with oblong nuclei, which we recognise as the connective tissue and corneal cells (_Plate VI, Figs. 2_ and _3_). The protoplasm of these cells is clear, while that of the round cells is more or less granular. The nuclei of the latter are also round, and usually very granular; the flat cells are much less stained by carmine than the round cells, and one sees the flat cells lying on connective tissue bundles. The nodules are richly supplied with blood vessels; in the nodules of the skin it cannot be determined whether the vessels are newly formed, or only those already present in the cutis. They are, however, always of embryonic type. One sees very plainly their formation from cells, and in the cornea, indeed, the vessels _must_ be newly formed. Here the vessels penetrate into the cornea before the nodule forms, and round these vessels, penetrating into the cornea, there are always visible collections of cells which are apparently migrated white blood corpuscles (_Plate VI, Fig. 4_).