CONTENTS vii PAGE IV. Viruses- Some Physicochemical Properties of Spontaneous Mouse Encephalomyelitis Virus, Strain Fa. By H. Leyon . . 217 By R. Markham . . 221 Physicochemical Studies of the Turnip Yellow Mosaic Virus. The Place of X-ray Diffraction Methods in the Estimation of the Size and Mutual Arrangements of Colloidal Particles. By J. D. Bernal and C. H. Carlisle . . 227 The Fine Structure of Protoplasm in Healthy and Virus-diseased Cells. By Ralph W. G. Wyckoff . . 230 Variations of the Size and of the Size Distribution of Tobacco Mosaic Virus Particles depending on the Method of Prep- aration. By J. Baudet, 0. Croissant, D. G. Dervichian, M. Joly and J. Moss& * 236 L GENERAL DIscuss1oN.-Dr. G. Oster, Dr. P. Johnson, Dr. R. Markham, Dr. D. D. Eley, Dr. C. E. Challice, Dr.R. D. Preston, Dr. H. Leyon, Dr. M. H. F. Wilkins, Dr. M. Joly . 247CONTENTS vii PAGE IV. Viruses- Some Physicochemical Properties of Spontaneous Mouse Encephalomyelitis Virus, Strain Fa. By H. Leyon . . 217 By R. Markham . . 221 Physicochemical Studies of the Turnip Yellow Mosaic Virus. The Place of X-ray Diffraction Methods in the Estimation of the Size and Mutual Arrangements of Colloidal Particles. By J. D. Bernal and C. H. Carlisle . . 227 The Fine Structure of Protoplasm in Healthy and Virus-diseased Cells. By Ralph W. G. Wyckoff . . 230 Variations of the Size and of the Size Distribution of Tobacco Mosaic Virus Particles depending on the Method of Prep- aration. By J. Baudet, 0. Croissant, D. G. Dervichian, M. Joly and J. Moss& * 236 L GENERAL DIscuss1oN.-Dr. G. Oster, Dr. P. Johnson, Dr. R. Markham, Dr. D. D. Eley, Dr. C. E. Challice, Dr. R. D. Preston, Dr. H. Leyon, Dr. M. H. F. Wilkins, Dr. M. Joly . 247