164 PATHOLOGY OF TYPHUS IN MAN 



of the lesion by fibroblasts on the twentieth and twenty-fourth 

 days. Lymphoid, plasma cells, and mast cells increase in num- 

 ber with the age of the nodule and phagocytosis of cells be- 

 comes more common. It is evident that repair takes place by 

 fibrosis, by avascular granulation tissue. 



(b) The heart: (Plates XVI and XVII, figs. 41 and 43.) The 

 portions of the myocardium selected for microscopic exami- 

 nation from each case were the interventricular septum near 

 the apex and the left ventricle wall at the base of and includ- 

 ing the anterior papillary muscles. 



Lesions are present in the slides of all of our cases, and with 

 few exceptions of a degree and character making possible the 

 recognition of processes due to typhus. 



Slight degrees of edema evidenced by changes in the con- 

 nective tissue septa and vacuolization of the muscle fibers is 

 present in several cases. 



The distinctive lesion is focal as described by Ceelen and 

 Nicol and presents as a discrete area, smaller than the " no- 

 dules" in skin and brain and most often present in the inner 

 half of the venticle wall. These lesions are most often in the 

 substance of the myocardium and in our series rarely in the 

 connective tissue septa. They consist of collections of cells 

 in which large amoeboid and phagocytic mononuclears (en- 

 dothelial cells) predominate; lymphoid and plasma cells are 

 numerous and mast cells and eosinophiles are fairly common. 

 Polymorphonuclear leucocytes are present in small numbers 

 and in large numbers when there is necrosis of muscle fibers 

 which is frequently the case in the area involved by this focal 

 lesion. The necrosis usually involves only a portion of one or 

 several muscle fibers. It is often impossible to recognize the 

 obliterated blood vessels in these focal lesions, on the other 

 hand capillaries filled with endothelial cells and frequently 

 with fibrin thrombi are found in early lesions. 



A more diffuse infiltration of the myocardium is invariably 

 present in the form of endothelial cells, lymphoid cells, and 

 plasma cells which lie packed between capillaries and (ap- 

 parently) normal muscle fibers. 



