RICKETTSIA IN TISSUES 189 



(v) The demonstration of rickettsia in human tissue: Early 

 in the study of the vascular lesions paired, ovoid, somewhat 

 lanceolate bodies were found in considerable numbers in 

 endothelial cells in situ. (Plates XXVIII and XXXII, figs. 

 68, 79, and 81.) These bodies are slightly smaller in size than 

 those in Rocky Mountain spotted fever, but in other respects 

 they are similar. They are found only in the endothelium 

 and never, as in Rocky Mountain spotted fever, in the smooth 

 muscle of the media. They are usually surrounded by a nar- 

 row clear zone or halo and the pairs measure slightly over 1 

 micron in length and 0.2 to 0.3 microns in width. (Plates 

 XXIX and XXXII, figs. 70, 73, and 82). They correspond 

 to the larger and more deeply stained pairs found in the louse. 

 When present in endothelial cells in numbers these larger 

 forms of paired rickettsia are arranged in rows following the 

 long diameter of the cell. (Plates XXVII, XXVIII, and 

 XXXII, figs. 66, 68, 79, and 81.) 



A more extended study showed that cells containing large 

 numbers of these deeply staining forms were rare, but that 

 on the other hand cells with one to several pairs were common. 

 (Plate XXIX, fig. 73.) 



Smaller paired forms, massed within cells as described in 

 Mexican typhus (Wolbach and Todd, 1920), were found in 

 nearly every case carefully studied (Plate XXVI, figs. 61, 

 62, and 63). This globular massing of the organisms is the 

 most characteristic appearance of rickettsia in human lesions. 

 (Plates XXVII, XXVIII, XXXI, and XXXIII, figs. 65, 69, 

 78, and 87.) 



The organisms stain with difficulty and it is sometimes neces- 

 sary to vary the technic of staining in regard to the reaction 

 of the water used for dilution of Giemsa's stain and in regard 

 to the degree of differentiation in order to get satisfactory 

 preparations. Frequently swollen endothelial cells, with cir- 

 cumscribed lightly staining granular areas, were found upon 

 restaining to contain masses of rickettsia occupying the areas 

 found appearing as lightly staining -and granular. In our 



