CHAPTER TWO 



THE SIZE, SHAPE, AND HYDRATION OF VIRUSES 



Very great advances in our knowledge of the size and shape 

 of viruses have been made in the past 15 years. Viruses are no 

 longer characterized as vague, filterable pathogenic agents but 

 today are thought of as having a definite i)hysical shape, which 

 in one or two cases is very accurately known. A large part of 

 this advance has been due to the ability to prepare virus that is 

 sufficiently concentrated to be seen with the electron micro- 

 scope, but other methods have also played a part. In this chap- 

 ter, we discuss the various available methods and give the more 

 striking results. A summary of methods of measuring virus size 

 was given by Markham, Smith, and Lea (194'2). 



Optical Microscopy 



Ultraviolet microscopy, using either reflecting or quartz optics, 

 can be carried out down to a wavelength of 2,000 A. This means 

 that resolution to about 2,000 A is possible, and some viruses 

 are sufficiently large to be seen in this way. Psittacosis can be 

 seen readily and its size determined; vaccinia can just barely 

 be seen, not adequately for confirmation of its shape. In actual 

 fact, modern techniques have not been applied sufficiently to 

 this old problem. The great advantage of optical microscopy 

 lies in the fact that the virus does not have to be dried and put 

 in a vacuum, and hence an idea of its shape under living con- 

 ditions can be obtained. 



Electron Microscopy 



The electron microscope has been of great value in virus 

 research. No matter how determined a virologist may be to 



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