THE MORPHOLOGICAL APPROACH 73 



lung epithelium, removed at frequent intervals after infection with large 

 amounts of psittacosis virus and carefully stained. Since most, if not all, of 

 the cells were infected, certain fairly definite conclusions could be made con- 

 cerning a cycle of development. Although this study was an extension of the 

 original observations of Bedson and Bland (1932), we will use the later 

 outline: 



1. During the first 8 hours an indeterminate stage occurs, during which 

 good elementary bodies are found on the outside of the cells, but no recog- 

 nizable changes inside. 



2. From 8 to 24 hours, a stage of homogeneous plaques is observed. These 

 are scanty and small and at first are found mainly at the tips of the cell 

 process. Later they become larger and more central. It is important to note 

 that these plaques are only apparently homogeneous, for after strong de- 

 colorization they are seen to consist of a pale pinkish matrix in which there 

 are lilac-colored elementary bodies. Thus, the plaques are considered as 

 colonies of the large forms of the virus. 



3. Between 18 and 24 hours, colonies of large forms are prevalent. 



4. From 24 to 48 hours, the picture becomes more varied. The colonies 

 contain particles of intermediate size and depth of color. 



5. From 48 hours on, the elementary bodies become more and more 

 numerous. The particles become more motile (Brownian movement), pre- 

 sumably because of a change in the viscosity of the matrix. 



Despite the valuable data which may be obtained from the study of 

 living infected cells, particularly when the virus is large enough to be seen 

 with a light microscope, there have been relatively few such studies of this 

 virus group. Gey and Bang (1939) cultured the virus of lymphopathia venerea 

 (lymphogranuloma) in a strain of a human fibroblast and found that 

 clear vesicles developed in cells some 12 days after inoculation. Enlarged 

 virus particles of a little less than 1 fi developed within the clear fluid, and 

 in turn developed into masses of smaller particles of about 0.2 /x, which 

 pushed the nucleus to one side, hypertrophied into masses several times the 

 size of the normal cell, and yet usually maintained an active Brownian 

 movement. Virus release took place with an obvious breakdown of the vesicle. 

 The process of infection was followed in the same cultures for more than 7 

 months. No plaques were described. Similar changes were later found in 

 malignant rat cell strains infected with the same virus (Bang and Gey, un- 

 published). Almost identical findings were reported independently by Manabe 

 (1939). 



B. Elementary Bodies 



Since the first descriptions of the tiny granules associated with this group 

 of viruses (Levinthal, 1935; Miyagawa et al., 1936), there has been a series of 



