214 DESCRIPTION OF PLATES 



PLATE VII 



FIGURE 24. Louse Box 60, Louse 2. Rickettsia prowazeki. 



Low power, photomicrograph. Section. This longitudinal section 

 through an experimentally infected louse shows the mid-gut filled with 

 debris from uncompleted digestion of blood. Most of the epithelial cells 

 of the mid-gut are apparently normal. Some of them are swollen and 

 distended. Such cells are infected with Rickettsia prowazeki. They are 

 very characteristic and can be easily recognized by examination under 

 the dissecting microscope. 



FIGURE 25. Louse Box 64, Louse 3. Rickettsia prowazeki. 



2,000 diameters. Low power, photomicrograph. Sagittal section 

 through an experimentally infected louse. The mid-gut is filled with 

 debris of partially digested blood. Some of the epithelial cells are ap- 

 parently normal. Most of them, especially at the anterior end of the 

 gut and the diverticulum (D), are heavily infected with Rickettsia 

 prowazeki and are greatly distended and swollen. Such an appearance 

 of the epithelial cells is characteristic of heavily infected lice. Such cells 

 are recognizable under the dissecting microscope. 



PLATE VIII 



FIGURE 26. Louse Box 57, Louse 4. Rickettsia prowazeki. 



1,200 diameter. Section of a louse's mid-gut. Enormously swollen 

 epithelial cells are shown. The clear areas probably represent collec- 

 tions of cell secretion. The remainder of the cells are filled with rickettsia 

 bodies single and paired. 



FIGURE 27. Louse Box 54, Louse 2. Rickettsia prowazeki. 



Low power. Section of the mid-gut of a louse. In only one small area 

 are the epithelial cells of the gut unswollen. Everywhere else the epi- 

 thelial cells are swollen, sometimes they are greatly swollen. All the 

 cells are heavily infected with rickettsia. The cell marked "A" is illus- 

 trated at higher magnification in Plate IX, figure 29. The two cells 

 marked "B" in Plate IX, figure 31. 



PLATE IX 



FIGURE 28. Louse Box 62, Louse 4. Rickettsia prowazeki. 



1,200 diameters. Section. Epithelial cell of a louse's mid-gut. Con- 

 tains rickettsia of varying forms. Cocci, diplococci, and rod forms, 

 singly and in short chains, are present. 



