CHAPTER Xll 



GYTOLOGIGAL CHANGES IN THE 

 INFEGTED HOST GELL 



This chapter is devoted to studies of visible changes in bacteria 

 caused by phage infection, and to the sequence of cytological 

 events during the latent period of intracellular phage multipli- 

 cation. These studies may be conveniently classified into cate- 

 gories on the basis of the technical methods used : ( 7) direct ob- 

 servation of living cells by dark field, ultraviolet, and phase con- 

 trast microscopy ; (2) observation of fixed and stained prepara- 

 tions to determine the succession of cytochemical changes; and 

 (3) observation in the electron microscope of fixed and dried 

 whole cells and of embedded and sectioned preparations to ob- 

 tain higher resolution than is possible in the first two techniques. 



All methods agree in demonstrating that marked changes oc- 

 cur in bacterial cells as a result of phage infection. A major 

 problem is the correlation in time of the events observed by the 

 various techniques, and almost as difficult is the elimination or 

 control of artefacts caused by the technical methods employed in 

 the preparation of specimens for observation. Other complicat- 

 ing factors include variation in the sequence of events with dif- 

 ferent phages attacking the same host strain, and variation in the 

 time required for intracellular virus growth under different en- 

 vironmental conditions, which make it more difficult to compare 

 the experiments of difTerent investigators. These technical 

 hurdles as well as the highly developed imaginations of the inves- 

 tigators are responsible for the great diversity of interpretations 

 which have been published. 



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