Scientists in cytological investigations study 

 the effects of viruses on animal cells, the loca- 

 tion of virus within cells, and the relationship of 

 cell changes to animal susceptibility and im- 

 munity. 



Changes in the various tissues and organs of 

 animals infected with viruses are studied by the 

 pathologists of this group. Although most for- 

 eign animal viruses cause disease signs that are 

 readily seen, there also are significant micro- 



scopic changes. Knowledge of all these disease 

 alterations is essential for recognition and dif- 

 ferentiation. 



In tissue-culture studies, practical methods 

 for producing large quantities of virus are being 

 developed for fundamental and applied research. 

 Virus-cell relationships also are studied by de- 

 veloping virus-susceptible cell cultures, special- 

 ized cell lines, and modification of virus by re- 

 peated passage in tissue culture. 



Physicist examines foot-and-mouth disease virus particles under the electron microscope. 



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