PATHOLOGICAL HISTOLOGY 161 



within capillaries and vessels of pre-capillary size are frequent. 

 We believe that cells in mitosis outside of blood vessels are of 

 endothelial origin as such cells can be seen fixed in the act 

 of migration. At this early period polymorphonuclear leu- 

 cocytes are fairly abundant in the connective tissue adjacent 

 to vessels with lesions. Some of the swollen endothelial cells 

 in situ (Plate XXVI, figs. 61 to 63 and Plate XXIX, figs. 70 

 to 73) possess a distinctive lightly stained appearance and 

 when carefully examined by high power in well stained prepara- 

 tions, they are found to contain great numbers of minute 

 paired lightly stained (blue) coccoid bodies (Plates XXVII 

 and XXXII, figs. 67 and 80), identical in appearance to the 

 rickettsia bodies in tightly packed cells of the louse's stomach 

 (p. 137). 



In skin taken in the fifth day of the disease, mural and oc- 

 cluding thrombi of fibrin are found in arteries and veins in the 

 lower layers of the corium. Circumscribed groups of cells 

 about vessels, the "nodules" (p. 159), are now present. (Plate 

 XIV, fig. 39.) We believe that these nodules are invariably 

 secondary to vascular lesions, or, that their location is always 

 determined by lesions of blood vessels. We have many times 

 seen vessels of pre-capillary size packed with swollen en- 

 dothelial cells and in such instances the wall of the vessels is 

 difficult to make out. Groups of occluded capillaries are to 

 be found in the "nodules" of the sub-papillary region and in 

 those replacing coil glands. The reaction about the coil gland 

 plexuses results in the disappearance of the glands. The 

 ensuing phagocytosis of degenerated epithelial cells by mono- 

 nuclears complicates the picture but furnishes evidence that 

 the majority of the mononuclear cells composing the early 

 typhus nodule are macrophages, otherwise called mononuclear 

 phagocytes and endothelial leucocytes. These cells in the 

 typhus "nodule" are characterized by a lightly staining 

 cytoplasm and give to the "nodule" a characteristic appear- 

 ance. Paired granules which we believe to be rickettsia are 

 frequently demonstrable within these cells in large numbers. 

 Other cells found this early in the typhus "nodules" are 



