ACKNOWLEDGMENTS 



I AM indebted to the following authors, editors and pub- 

 lishers for their permission to reproduce figures which have 

 appeared in the literature: Fig. 3.1, Prof. A. L. Audus and 

 Fig. 10.2, Dr. P. Mitchell, and the Editors of Nature; Fig. 

 3.2, Prof. J. H. Quastel and Dr. P. G. Scholefield, and 

 Messrs. Williams and Wilkins Co., U.S.A.; Fig. 4.1, Prof. 

 P. W\ Wilson and the Editors of the Biochemical Journal', 

 Figs. 6.1 and 6.2, Dr. E. F. Gale, F.R.S., the Academic 

 Press Inc., U.S.A., and the Editors oi t\\t J ounml of General 

 Microbiology; Fig. 8.1, Prof. L. Gorini and Prof. CI. Fro- 

 mageot, and the Elsevier Publishing Co., Inc.; Plate I, Dr. 

 B. Davis and the Editors of Experientia; Plate III, Prof. R. 

 Tulasne and Dr. R. Vendrely, and the Long Island Bio- 

 logical Association: Plate II is a photograph of a chromato- 

 gram kindly prepared by Dr. R. Markham. 



