162 PATHOLOGY OF TYPHUS IN MAN 



polymorphonuclear leucocytes and mast cells; the lattef'occur 

 in increasing abundance as the disease advances. (Plates 

 XIV and XV, figs. 39 and 40.) 



Mural thrombi in arterioles and venules with very little 

 peri vascular reaction are found in the fifth day. The earliest 

 indication of thrombus formation consists of masses of blood 

 platelets massed upon and apparently within swollen endothe- 

 lial cells in situ. Small fibrin thrombi apparently form upon 

 such platelet collections while the underlying endothelial 

 cells remain viable. We interpret the process as one affecting 

 the cytoplasm of the endothelial cell in such a way, perhaps 

 by a change in viscosity, as to attract the platelets. Whatever 

 the interpretation, the fact is that microscopic mural thrombi 

 are frequent and become at this early stage completely sur- 

 rounded by endothelium. (Plate XIII, fig. 37.) The endothe- 

 lial cells at the base of the thrombus frequently contain masses 

 of rickettsia (Plates XXVII and XXVIII, figs. 83, 85, and 86). 



Changes subsequent to the fifth day consist in a further 

 development of the nodules and involvement of larger blood 

 vessels, arteries, and veins in the lowest layer of the corium 

 and in the subcutaneous fat. (Plate XII, fig. 36.) Occluding 

 thrombi of large vessels are excessively rare; mural thrombi 

 exist in vessels without severe damage to the media; indeed 

 the muscular coat of blood vessels shows only the presence of 

 migrating cells, and necrosis of individual muscle cells ap- 

 parently secondary to the accumulation of migrating cells, 

 mononuclear and polynuclear. Here again we have a contrast 

 to the vascular lesions of Rocky Mountain spotted fever, 

 where severe damage to the media occurs. 



In addition to the "nodules," a diffuse perivascular infil- 

 tration is invariable in skin from typhus. The cells composing 

 this diffuse infiltration are mononuclear phagocytes (en- 

 dothelial leucocytes), lymphoid and plasma cells, mast cells, 

 and rarely polymorphonuclear leucocytes. Mast cells are 

 strikingly abundant. Polymorphonuclear leucocytes persist 

 in fair numbers in the typhus " nodules" until reparative 

 changes have begun. Their presence we believe is wholly in- 



