96 
the fibrin masses and cells may be distinguished. The process near the 
surface may therefore be said to represent an extensive coagulation necro- 
sis. When the lesion is examined with the naked eye, these homogeneous 
necrotic masses of tissue, in which much fibrin is deposited, give rise over 
portions of the surface of the ulcer to the very striking pseudomembranous 
appearance, already referred to, Deeper still in the section the connective- 
tissue cells are seen to be very greatly proliferated and in places plasma 
cells are plentiful in number. In other portions of the tissue, the con- 
nective-tissue fibers are pushed apart, and there are other evidences of 
inflammatory adema. Between these fibers may be seen a few small 
round cells, red-blood corpuscles, and polymorphonuclear leucocytes. The 
condition of the blood vessels in which there is a considerable proliferation 
of the perithelial cells, is quite striking in these areas of inflammatory 
wdema. The process is particularly well marked about the veins. In 
many of the vessels the polymorphonuclear leucocytes within their lumina 
are increased in number, and sometimes these may be seen lying between 
the several layers of the meso and perithelial cells, which partly form 
the wall of the vessel. Near these areas large multinuclear giant cells 
are occasionally observed. Very few eosinophiles are present, and only 
occasionally a plasma cell is here seen. Scattered through the section are 
numerous other areas of necrosis, in which, generally, considerable fibrin 
is present and in which there are also numerous red-blood cells, small 
round cells, polymorphonuclear leucocytes, fragmented nuclei, much 
granular material, and many bacteria. Eosinophiles are not seen in these 
situations ; but bacilli, which only partly decolorize by Gram’s stain, and 
cocci, which retain the latter, are encountered usually lying between the 
cells. No bodies resembling protozoa and no tubercle bacilli appear to be 
present. In a section at the edge of the ulcer, which includes some of 
the epidermis, the cells of the Malpighian layer are proliferated. Jn 
places, this layer is extensively infiltrated and sometimes apparently 
destroyed, the area of infiltration and necrosis reaching from below up- 
ward to the corneal layer, which it touches. Evidently in this way new 
foci of ulceration are formed. In centain areas the corneal layer has 
entirely disappeared. In these places of necrosis an appearance similar 
to that which has been described in regard to the subcutaneous tissue is 
seen—coagulation necrosis, deposits of fibrin, fragmented polymorphonu- 
clear leucocytes, ete. The papillary and reticular layers are also ex- 
tensively infiltrated with round cells and polymorphonuclear leucocytes ; 
in addition both of these strata contain areas of necrosis similar to those 
already described. The histological appearances are pictured in figs. 
15 to 18. 
The lesion in the monkey histologically consists of an abscess cavity in the 
corium and subeutaneous tissue, about which there is little which is characteristic. 
The pathological changes encountered appear in many ways similar to those seen 
in the human lesion; but the process is less chronic and there is no proliferation 
