184 PATHOLOGY OF TYPHUS IN MAN 



leaving cicatrices, by degeneration and migration of the cells. 

 But a few cicatrices are left in the form of spindle shaped cells 

 (neuroglia ?). Our own observations lead us to believe that 

 the lesions following the disappearance of the cells are replaced 

 by small amounts of fibrillary neuroglia. 



Other smaller loose-textured lesions are common, both in 

 human and animal tissues in the superficial layer of the cerebral 

 cortex (Plate XXIII, fig. 55) and in the molecular layer of the 

 cerebellum. (Plate XXIV, fig. 58.) Some of these lesions we 

 identify as the rosette lesions mentioned by Spielmeyer, others 

 take the form of irregularly arranged, many processed, and 

 apparently anastamosing glia cells occupying areas 0.05 to 

 0.1 millimeters in diameter and arising we believed by the 

 proliferation of pericapillary neuroglia cells. 



These various lesions of the central nervous system repre- 

 sent a definitely proliferative reaction preceded by injury to 

 and probably always by a proliferation of the endothelium of 

 capillaries and pre-capillaries. The lesions are composed chiefly 

 of two elements, cells derived from the vascular endothelium 

 and from the neuroglia. The lesions are invasive in character 

 in that they lie in the substance of nervous tissue. Vascular 

 lesions determine solely the sites of these proliferative lesions. 

 The evidence at hand points to the conclusion that the endo- 

 thelial and neuroglial proliferation is in direct response to the 

 presence of the parasite of typhus, carried we believe into the 

 nerve tissue by the migration of endothelial cells. The actual 

 demonstration of rickettsia in the endothelial cells of blood 

 vessels in situ in the brain has been accomplished by us in hu- 

 man and animal tissues. The presence of fine granules in the 

 neuroglia cells of the lesions makes the recognition of rickettsia 

 in this location uncertain, though in the guinea-pig there are 

 masses of paired granules within cells and lying apparently 

 between cells which we believe are rickettsia. Clusters of 

 bodies like that illustrated in Plates XXVIII and XXX, figures 

 69 and 75, we accept without reservation as rickettsia. 



Hemorrhages in the central nervous system in typhus are 

 usually limited to the perivascular spaces. Occasionally, how- 



