182 PATHOLOGY OF TYPHUS IN MAN 



The next stage in the development of the lesion is .the ap- 

 pearance of mononuclear cells around the affected capillary or 

 pre-capillary. When the vessel wall remains in evidence, as it 

 frequently does, as a delicate pink staining hyaline structure, 

 these mononuclear cells seem to have an extra-vascular origin. 

 We have frequently seen cells which are universally regarded 

 as perivascular neuroglia cells in mitosis immediately adjacent 

 to thrombosed capillaries. On the other hand, the occurrence 

 of phagocytic cells early in the formation of the lesion reveals 

 the presence of macrophages (endothelial leucocytes) and we 

 believe that these cells of mesenchymal origin play an impor- 

 tant role in the early lesion. 



The reaction of neuroglia seems almost simultaneous with 

 that of the endothelium, and the small nodules consist of both 

 of these elements. (Plate XXII, fig. 54.) Polymorphonuclear 

 leucocytes are invariably present in small numbers. In the 

 adjacent brain tissue we find at this early stage the presence 

 of elongated cells directed radially towards the lesions, cells 

 which by virtue of their shape and granular cytoplasm are 

 identified as types of neuroglia cells, the "rod cells." Satellite 

 cells in apposition to ganglion cells immediately adjacent to 

 the lesions show swollen nuclei; and forms indicative of 

 migration towards the lesion are common. There is also an 

 increase in number of satellite cells in the zone adjacent to 

 the lesion and ganglion cells involved in the periphery of the 

 "nodule" undergo neuronophagia. The lesion increases in 

 size by the accession of mononuclear cells with abundant 

 cytoplasm. Many of these cells have shapes and processes 

 indicative of neuroglial origin; and with the phosphotungstic 

 acid hemotoxylin stain the cytoplasm appears homogeneous 

 and to contain, near the nucleus, prominent centrosome-like 

 bodies in pairs and clusters. With Giemsa's stain the cyto*- 

 plasm of these cells appears in many instances to be filled with 

 minute deep blue staining granules. Whether rickettsia bodies 

 are included cannot be proved, as the cytoplasmic granulation 

 cannot be differentiated from that found in neuroglia cells in 

 other types of reactions. 



