PREFACE 



This collective volume is intended to serve as a stimulating but 

 critical guide to that rapidly growing group of scientists who must 

 resort to physical methods of research for the solution of biological, 

 medical, and agricultural problems. 



Each chapter provides an authoritative orientation with respect 

 to one general research method. To achieve this end, each chapter 

 covers the following points: (1) the fundamental principle of one 

 method, its underlying assumptions, and perhaps a simple mathe- 

 matical outline of the theory involved; (2) the tj'^pes of problems for 

 which the method offers promise of a unique solution or a helpful 

 approach; (3) the demands made on apparatus, materials, and 

 technical skill; (4) the limitations of the method in some detail; 

 and (5), briefly, its outstanding accomplishments to date. After 

 reading any chapter, a scientist should be able not only to appraise 

 the potentialities of its method with reference to his own biological 

 problem, but also to understand the limiting factors that must be 

 given recognition in the proper design of critical experiments. 



The book should prove useful in a wide variety of advanced 

 courses, particularly for collateral reading assignments aimed at the 

 mature student. Each chapter can be read as an independent unit 

 without regard to its position in the volume. 



References to commercial sources of equipment and materials have 

 been included by the several authors as a convenience to the reader. 

 Listing of a product and its source does not necessarily constitute 

 an endorsement nor does failure to list a product indicate its inferiority 

 in any way. 



My thanks are willingly expressed to the several authors for their 

 kind cooperation at all stages of the work. Others who offered 

 helpful suggestions during the planning stage include: Dr. L. R. 

 Blinks, the late Dr. S. C. Brooks, Dr. C. S. French, Dr. D. R. God- 

 dard, Dr. W. M. Stanley, Dr. Otto Stuhlman, and Dr. Maurice 

 Visscher. Most of the editorial work was accomplished while I was 

 Professor of Physics at Iowa State College. C-onsecjuently, I feel 

 most indebted to the Department of Physics at Iowa State College 



