CYTOLOGICAL CHANGES IN THE INFECTED HOST CELL 205 



vacuole in turn containing a dense central object which is inter- 

 preted to be a coil of tightly wound threads. The vacuoles oc- 

 cupy positions in the cell corresponding to the nuclear bodies 

 seen in stained cells. Cells fixed 4 to 8 minutes after infection 

 showed considerable rearrangement. The nuclear areas, in 

 particular, were replaced by similar foci (containing elongated 

 dark bodies) at the periphery of the cells. The uncertainties of 

 fixation and damage during polymerization of the embedding 

 plastic must be considered as major difficulties to be solved be- 

 fore really useful preparations and interpretations can be ex- 

 pected (see Maal0e and Birch-Andersen, 1956). 



A defect in the interpretation of much of the work with the 

 electron microscope is the tendency of the technologist to arrange 

 his photographs in what seems to him to be a logical sequence. 

 Even when samples for examination are taken serially during the 

 latent period, it may be impossible to arrange them in true tem- 

 poral order. This is in part due to difficulties in starting and 

 stopping the infectious process simultaneously in all cells and in 

 part because, even when trouble is taken to synchronize phage 

 development in the population of infected bacteria, the develop- 

 mental process soon gets out of phase in the individual cells 

 (Benzer, 1952). However, probably none of the difficulties is 

 insuperable, and current technical developments lead one to 

 hope that micrographic work will contribute greatly toward an 

 understanding of viral growth. 



4. Summary 



Phage multiplication is accompanied by major changes in the 

 cytology of the host bacteria. Bacterial multiplication stops, in 

 some cases immediately after phage adsorption but in other sys- 

 tems only after one or two cell divisions. In most systems there 

 is an enlargement of the bacterial cells during the latent period. 

 The release of phage which terminates the latent period is usually 

 accompanied by an abrupt disintegration of the cells. In a few 

 cases where the bacterial cell walls seem to be unusually sturdy, 

 lysis involves a slow collapse of the cell with leakage of the cyto- 



