'^^\^Ai 





CONTENTS 



Foreword v 



I. The Nature OF Viruses AND Their Relation TO Physics. . . 1 



Introduction 1 



Outline of Virology 2 



Virus Multiplication 3 



Size and Shape of Viruses 4 



Mutation of Viruses 5 



Mutual Interference of Viruses 6 



Virus Attenuation After Multiple Passage 6 



Chemical Composition of Viruses 7 



Virus Serology 8 



Hemagglutination 9 



Purified Virus Preparations 10 



Virus Assay 10 



Origin of Viruses 12 



Physics and the Study of Viruses 13 



II. The Size, Shape, and Hydration of Viruses 15 



Optical Microscopy 15 



Electron Microscopy 15 



Ultrafiltration 22 



Observations of the Motion of Viruses 24 



Diffusion 25 



Sedimentation 29 



Sedimentation Technique 34 



Diffusion-Constant Measurement During Sedimentation 38 



Hydrated Partial Specific Volume 38 



Viscosity 40 



Asymmetric Particles 43 



Examples of the Use of Virus Motion Studies 45 



X-Ray Diffraction Applied to Viruses 54 



Small-Angle X-Ray Scattering by Viruses 58 



Picture of a Virus 62 



Identity of Physical Particle and Infectious Unit 62 



Virus Dimensions 65 



III. Ionizing Radiation and Viruses 69 



Nature of Energy Loss by Fast Charged Particles 70 



Space Distribution of Primary Ionizations 74 



Experimental Methods and Some Results 77 



ix 



