THE MORPHOLOGICAL APPROACH 87 



was increased until it reached amounts exceeding that in the controls. Heat- 

 inactivated virus caused a distinct increase in DNA during the first half hour 

 of infection, after which the content returned to normal. As the author points 

 out, these changes in DNA are hard to interpret in relation to virus synthesis, 

 since the virus contains little or no DNA. They may be part of the cell's 

 reaction to cytoplasmic events. The need for studies similar to this on other 

 cell virus systems, particularly a type of tissue culture in which most of the 

 cells can be infected simultaneously, is obvious. 



E. Electron Microscopy 



The first electron microscope study of respiratory epithelium infected 

 with influenza is that of Harford et al. (1955), in which mouse bronchial 

 epithelium was used. It is particularly valuable because it is a continuation 

 of a careful study (Harford and Hamlin, 1952) of the same lesions by light 

 microscopy. In both studies it is apparent that many ciliated cells persist at 

 the height of the lesion and that certain intracytoplasmic inclusions are 

 definitely present in the ciliated cells. An electron microscope study of the 

 ferret mucosa (Hotz and Bang, 1957a), in which much more ciliated epi- 

 thelium is destroyed, raises several comparative points. Since dead ciliated 

 cells seem to be readily sloughed out into the lumen, or phagocytized, it is 

 possible that a high proportion (even half) of the ciliated cells was destroyed 

 and sloughed away early, leaving the adjacent, less-affected cells behind. 

 Secondly, phagocytized material, particularly degenerating cytoplasm, 

 would simulate in many ways the microscopic picture described by Harford 

 et al. These questions would seem open until combined microspectrophoto- 

 metric measurement of DNA, electron microscopy, and fluorescent antibody 

 studies were all done in the same cell system. 



The electron microscope study of ferret mucosa (Hotz and Bang, 1957a) 

 infected with influenza showed details of cell destruction and disintegration 

 which included a ballooning of the lamellar system of the cells (endoplasmic 

 reticulum) and of the mitochondria, and the accumulation of fluid between 

 the nuclear and cytoplasmic portions of the "nuclear" double membrane. 

 The process of regeneration of cilia could be observed, but no specific virus 

 effects were found. 



F. Fluorescent Antibody Staining 



This important new technique, developed by Coons and Kaplan for antigen 

 localization, has been used to study the viruses of mumps (Watson, 1952), 

 influenza (Watson and Coons, 1954), and Newcastle disease (Burnstein and 

 Bang, 1958) in the chorioallantoic sac of the chick embryo. It has also been 

 used by Liu (1955a,b) to study influenza in the ferret mucosa and human 



