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PATHOLOGICAL ANATOMY in the supporting tissue. The same cell elements occur but they are now characterized mainly by the increase in the amount of their protoplasm (Plate I, Fig. 4). This figure consists of two parts, which are separated by a diagonal light zone due to shrinking of the preparation. The upper part shows a tissue infiltration; the lower, in which the round cells are denser, shows an exudate around a small branch of the same central vessel, from which the infiltration of the lymphatic space depicted in Fig. 3 was obtained. These infiltrations are continuous and arise from the same infiltration. The same cells as have already been mentioned, lymphocytes, leucocytes and polyblasts, are present in this figure. The polyblasts now consist of immense cell masses, possessing a light staining reticulated nucleus and abundant protoplasm; they are here in greater number and show a still higher development than before. In the tissue infiltration, two isolated glial nuclei and one leucocyte can be observed, but no typical lymphocytes. Lymphocytes can, however, be seen in the adjoining vascular infiltration.

Obviously, the relative numbers of lymphocytes, leucocytes and polyblasts are not everywhere the same as is here depicted. In some places the lymphocytes are in the majority ; in others, the leucocytes. As a rule, however, in the tissue infiltration, the mass of the round cells consists of polyblasts. Pirie and I arrived at this conclusion almost simultaneously.

Another interstitial change which plays an important part in the appearance and disappearance of the symptoms has yet to be considered, namely edema. To the naked eye, in many cases, edema is obvious. Indeed it is generally easier to detect macroscopically than microscopically. It is at least partly responsible for the appearance, which the glial tissue often presents, of being permeated by or converted into a finely granular substance. Sometimes the tissue seems to be loosened, so that the glial meshwork appears wider. In a few of Wickman's cases, circumscribed foci of softening were present in Clarke's column. In the lighter parts of Plate II, Fig. 6, only the remains of the delicate glial reticulum can be perceived. Biilow-Hansen, Harbitz, Forssner, Sjovall and others also describe a sponginess of the tissues. I think the edema is of no slight importance from a clinical point of view, as it affords a plausible explanation for the rapid disappearance of a paralysis. The dread change which gives rise to the paralysis has its seat in