72 F. B. BANG 



Intranuclear inclusions have been induced in cells with a variety of 

 chemicals (Blackmail, 1936). Deoxyribonucleic acid was not found in these or 

 in cytoplasmic inclusions induced in the same way (Wolman, 1954) (1955), 

 but, as will be pointed out later, it is also absent from the late lesions of a 

 typical "intranuclear virus" such as herpes. 



IV. Bacterial and Rickettsial Infections 



Although detailed studies of the pathology of cultured cells are not ex- 

 tensive in bacterial or rickettsial infections, a brief review is instructive. 

 Bacteria may be ingested and may accumulate in great numbers in cells 

 without destroying the host cell (Fell and Brieger, 1947), or they may be 

 digested fairly rapidly if nonpathogenic (M. R. Lewis, 1923), or they may 

 rapidly destroy the host cell (M. R. Lewis, 1920). 



The behaviour of rickettsia in living rat fibroblasts has even closer analo- 

 gies with the effects of viruses. Rickettsia rickettsii remains scattered through 

 the cytoplasm and causes fairly rapid degeneration of the host cell; it also 

 penetrates into the nucleus of the host cell. R. tsutsugamushi, on the other 

 hand, tends to accumulate in a mass near the nucleus and does not cause 

 gross morphological changes in the host cell for 8 or 9 days. The rickettsiae 

 are fairly frequently found extruded in the microfibrils, which are often 

 formed by these cells (Schaecter et al., 1957). 



R. burneti was studied in chick heart and skeletal fibroblast cultures 

 (Kausche, 1952). In these host cells, large and small clear vacuoles were 

 formed and within them were long chain forms of rickettsia. The nucleus 

 was pushed to one side by the enlarging vacuoles. When Aureomycin was 

 added, the vacuoles disappeared. Photomicrographs taken at 257 m/x 

 (ultraviolet) showed very dark nucleoli, presumably indicating an increase in 

 nucleoprotein metabolism. Electron microscope studies of thin sections of 

 R. mooseri (Wissig et al., 1956) in yolk sac showed the rickettsiae in meso- 

 thelial and epithelial cells, but not in fibroblasts, macrophages, or vascular 

 cells. The rickettsiae merely seem to grow and replace the host cell with 

 little reaction, leaving a pycnotic nucleus and a few mitochondria which 

 showed no lesions even when they had been greatly reduced in number. 



V. Psittacosis Group Viruses (Miyagawanella) 



A. Tissue Culture Stages 



The development of the viruses of this group in cells was clearly described 

 before the advent of the electron microscope. Furthermore, Bland and Canti 

 (1935) had been able to follow part of the developmental sequence in in- 

 dividual living cells. This was combined with a study in tissue culture of chick 



