DESCRIPTION OF PLATES 215 



FIGURE 29. Louse Box 54, Louse 2. Rickettsia prowazeki. 



1,200 diameters. Section. A swollen epithelial cell of a louse's mid-gut. 

 This is an illustration, at a higher magnification, of the cell marked 

 "A" in Plate VIII, figure 27. One end of the cell is filled with a granu- 

 lar mass of rickettsia among which occur scattered paired forms. At 

 the other end of the cell the rickettsia, in chains, are characteristically 

 disposed in a tress-like skein. 



FIGURE 30. Louse Box 54, Louse 1. Rickettsia prowazeki. 



1,800 diameters. Section. Swollen epithelial cell of the mid-gut con- 

 taining bacillary forms of rickettsia. The organisms are usually ar- 

 ranged in skeins of thread-like chains. They also occur singly, in pairs, 

 and in short chains. Lying free in the lumen of the gut is a short rickett- 

 sia thread. 



FIGURE 31. Louse Box 54, Louse 2. Rickettsia prowazeki. 



1,200 diameters. Section. Swollen cells of a louse's mid-gut. This is an 

 illustration, at a higher magnification, of the cells marked "B" in 

 Plate VIII, figure 27. Both cells are filled with minute rickettsia which 

 occur singly or in pairs. Scattered throughout the cells are larger 

 paired forms. The clear areas in these cells probably represent collec- 

 tions of cell secretion. Over such areas the forms of discrete rickettsia 

 granules are clearly seen. 



FIGURE 32. Louse Box 53, Louse 3. Rickettsia pediculi. 



1,200 diameters. Section. The epithelial gut cells contain no organisms. 

 Many riskettsia bodies are thickly placed over the surface of the cuticu- 

 lar border of the cells; this is well seen in one cell where, in sectioning, 

 the cuticular border has been cut tangentially. The lumen of the gut 

 is filled with partly digested blood. In the gut contents occur bacilli- 

 form crystals and spherical bodies which are colored with hemoglobin. 

 Many rickettsia bodies occur everywhere in the lumen of the gut. They 

 always occur as granules either singly or in pairs; they do not show 

 the wide variation in form which is exhibited by Rickettsia prowazeki. 



PLATE X 



FIGURE 33. Louse Box 64, Louse 3. Rickettsia prowazeki. 



1,200 diameters. Section. Junction of the esophagus and mid-gut of 

 a louse. The epithelial cells of the esophagus are not infected. The 

 epithelial cells of the mid-gut are greatly swollen and are heavily infected 

 with rickettsia. Most of the intracellular rickettsia are granular. Near 

 the base of the membrane of the gut, on either side of the esophageal 

 orifice, are small groups of bacilliform rickettsia. 



