1. Skin: Rocky Mountain Spotted Fever Lab 9, Case 1

2. Skin biopsy Note area of hemorrhage (arrow) in the dermis

3. Hemorrhage immediately underneath the epidermis Also note the cellularity and thrombosis of the small vessels in the dermis (arrow)

4. Small vessel in the dermis with mild vasculitis

5. Dermal vessel with mild vasculitis

6. Dermis with an area of more severe vasculitis (arrow)

7. Severe vasculitis in the dermis

8. Dermal vessel (arrow) which is exhibiting vasculitis and thrombosis

9. Thrombosed vessel in the dermis Note that the endothelial cells are missing along part of the circumference of the vessel (arrows). This is where the main part of the thrombus has attached. Also note the inflammation surrounding the vessel.

10. Brain: Bacterial Meningitis Lab 9, Case 2

11. Autopsy specimen Purulent exudate (arrows) in the leptomeninges

12. Exudate (1) in the meninges and congestion in the vessels (2) in the leptomeninges

13. Congested blood vessel Inflammatory exudate is present within the vessel and throughout the leptomeninges

14. Sulcus Congested vessels and inflammatory exudate in the leptomeninges

15. Inflammatory exudate within a sulcus The majority of cells in this exudate are neutrophils. There is also abundant fibrin (arrows) and red blood cells are present in the congested vessels.

16. A blood vessel from the previous image The vessel is surrounded by neutrophils (arrows).

17. Exudate from the leptomeninges which has been Gram-stained Note the Gram-negative bacteria (arrows) throughout this section.

18. Brain tissue with diffuse edema

19. Trachea: Diphtheria Lab 9, Case 3

20. Trachea with diptheritic membrane (1), which has pulled away from the tracheal lining during histological processing Note the tracheal cartilage (2) present in this section.

21. Trachea with diptheritic membrane (1) Even though the main part of the membrane has pulled away from the tracheal lining during histological processing, in this section part of the membrane is still loosely attached. Once again, note the tracheal cartilage (2).

22. Tracheal mucosa and diptheritic membrane The mucosal surface of the trachea is ulcerated (total loss of epithelial cells) and the only remaining epithelial cells are found in the glands (arrows). The diptheritic membrane consists of fibrin and inflammatory cells, most of which are dead.

23. Higher power of previous image showing the ulcerated tracheal mucosa and the diptheritic membrane Although difficult to make out at this magnification, most of the cells in this inflammatory exudate are neutrophils.

24. Heart: Acute Rheumatic Myocarditis Lab 9, Case 4

25. Mitral valve demonstrating marked thickening and fibrosis of the valve leaflet There are also numerous foci of fibrinoid necrosis within the cusps and friable vegetations (verrucae) along the lines of closure (arrows). These irregular, warty projections are found at sites of erosion on the inflammed endocardial surface. The verrucae probably result from the precipitation of fibrin where the leaflets impinge on each other.

26. Relatively normal looking heart tissue

27. Cellular accumulations- Aschoff bodies (arrows)- within the interstitum of the myocardium These are found especially around blood vessels.

28. Myocardium containing Aschoff bodies (arrows) within the intersitium

29. Cellular detail of Aschoff bodies Aschoff bodies are foci of fibrinoid necrosis surrounded by lymphocytes, macrophages, an occasional plasma cell, and plump “activated” histiocytes called Anitschkow cells or Aschoff cells (arrows). These distinctive cells have abundant amphophilic cytoplasm and central round-to-ovoid nuclei in which the chromatin is disposed in a central, slender, wavy ribbon resembling a caterpillar (hence the designation “caterpillar cells”).

30. Myocardium Cellular detail of Aschoff body In this case there appears to be a multinucleated Aschoff giant cell (arrow).

31. Clostridial Myonecrosis Lab 9, Case 5

32. Taken at autopsy Notice the swelling and the area of primary infection (arrow)

33. Hemorrhagic blebs (arrows) on the skin The blebs on the skin are accumulations of gas being discharged into the tissues from the Clostridium perfringens. The gas produces crepitance.

34. Muscle fascicles containing large gas bubbles (arrows) Note that there is no inflammatory reaction in this section.

35. Skeletal muscle The muscle cells are hypereosinophilic and most do not contain nuclei, indicating these cells are dead or dying. The round clear spaces (1) in this tissue correspond to gas accumulations prior to death. In between the bundles of muscle cells, accumulations of small dark blue-staining bacterial organisms can be seen (2). Also note that there is no inflammatory response in this tissue.

36. Gas accumulation is present in this tissue.1: Necrotic muscle cell 2: Mild inflammatory response3: Thrombosed blood vessel The blue-staining rods (bacterial organisms) can barely be appreciated at this magnification.

37. Higher-power of previous image provides clearer view of gas bubbles in the tissue, the necrotic hypereosinophilic muscle cell (1), and the mild inflammatory reaction (2) At this magnification, the bacteria located throughout this section can be better appreciated.

38. Stained with tissue Gram stain (Brown and Brenn) The Gram-positive bacilli can be seen throughout this section.

39. Actinomycosis Lab 9, Case 6

40. Retroperitoneal abscess At this magnification, multiple dark-staining foci can be appreciated. These foci are Actinomyces colonies (arrows). These colonies are known as “sulfur granules” because in gross specimens they are visible to the naked eye as yellow grains, thus resembling grains of sulfur.

41. Abscess demonstrating a pocket of purulent exudate that contains numerous actinomycotic colonies (arrows).

42. Actinomycotic colonies in the abscess

43. The filamentous nature (arrows) of the actinomyces organisms in these colonies can be appreciated.

44. Actinomycotic colony The filamentous nature (arrows) of the actinomyces organisms is more easily appreciated.