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20 ACUTE POLIOMYELITIS white matter, as well as in the anterior, posterior and lateral horns ; it is most constantly observed in relation to the sheaths of the blood vessels but, as Redlich first recorded, it may be seen also in small groups within the nerve tissue. I, myself, demon- strated in almost all of my early cases minute and rare foci of cell infiltration among the white nerve fibers. (Plate II, No. 2.) Such a small focus is pictured in the entrance zone of the pos- terior root. Diversity of opinion still prevails concerning the na- ture and origin of these round cells. While Rissler, Redlich, Schmaus, Harbitz, Scheel and others described them as migrated leucocytes, Goldscheider, recently joined by Strauss, maintains they are proliferated fixed tissue elements. The former have focused their attention principally upon the glia cells; the latter, upon the cells of the adventitia. According to Marburg, all are lymphocytes.

In my latest study of the pathologic anatomy of this disease, I think I have solved the problem of the nature of these cells. The principal cells are not leucocytes, nor proliferated connective tissue elements, nor are they simply lymphocytes. They represent a further stage in the development of the lymphocyte and are what Maximov has described as polyblasts. The distinguishing fea- tures of these cells are shown distinctly in the preceding plates. Plate I, Fig. 3, represents the exudate around the wall of a large- sized vessel. To the left can be seen only one cell, whose proto- plasm remains unstained (stain, Pappenheim's methyl, green and pyronin) ; four are obviously polynuclear leucocytes. The re- maining round cells can be divided into two groups, one of typical lymphocytes, encircled by a small amount of pink staining proto- plasm and containing a dark staining nucleus, rich in chromatin, which is aggregated at points into masses, the other of cell ele- ments which evidently are derived from lymphocytes, in which the nucleus stains lightly, in which a dainty network distinctly appears, and in which the protoplasm has increased. These cells later develop into types — as is evident from three or four of the larger forms in this figure — which have no resemblance to the mother cells, to which, however, numerous intermediate forms link them. The origin of these cells from lymphocytes' may therefore be con- sidered as proved.

Let us now pass to the infiltration around the small vessels and