172 PATHOLOGY OF TYPHUS IN MAN 



the histological elements of normal marrow are present in 

 proportions within the normal range. In a few cases with 

 extensive bronchopneumonia there are increased numbers of 

 polymorphonuclear leucocytes and "granular myelocytes pres- 

 ent. Megakaryocytes are present as in normal marrow. 



In the marrow of one case a small artery contains a throm- 

 bus. In a few marrows there are in addition to the usual blood 

 forming activity an increased phagocytosis of erythrocytes 

 and in capillaries and venules accumulations of phagocytic 

 mononuclear cells (endothelial leucocytes). 



An observation perhaps of interest is that in the four mar- 

 rows showing the earliest degrees of activity the presence of 

 small groups of marrow cells, pre-myelocytes and myelocytes, 

 is usually attended by the presence of delicate fibrin strands 

 and the fat cells are separated apparently by a liquid which 

 has yielded a finely granular precipitate. This we regard as 

 probably a regular concomitant of the early development of 

 activity. 



(n) The skeletal muscles: (Plate XVI, fig. 42.) Pieces of 

 muscle were sectioned for histological study from thirty-six 

 cases. The muscles selected for examination were the biceps, 

 rectus abdominalis, and quadriceps extensor group. 



Lesions of the blood vessels were found in all cases but one. 

 The vascular lesions are like those of the skin. In one case 

 with early thrombi in an artery rickettsia were found in 

 abundance in the endothelium. Extensive perivascular ac- 

 cumulations like those in the skin are the rule with vessels 

 containing lesions. A diffuse infiltration, like that in the 

 myocardium, of lymphoid, plasma cells, and eosinophiles 

 between muscle fibers is common but not constant. Degener- 

 ated muscle fibers in or adjacent to the perivascular lesions 

 are common; the appearances of these individual fibers is that 

 of Zenker's degeneration, and in late cases we have regenera- 

 tive changes in the sarcolemma. 



In one case there was fairly extensive waxy degeneration 

 (cf. p. 157) (Zenker's degeneration) of the rectus muscle. 

 This case was one with extensive bronchopneumonia, and the 



