PREFACE TO THE THIRD EDITION 



The request by The Wilhams & Wilkins Company to prepare a Thh-d Edition 

 so soon after the Second Edition was pubhshed (1948) was unexpected. It would 

 have been a simple matter for them simply to reprint the Second Edition in 

 whatever number they thought that they could sell within a reasonable period. 

 This, however, would have been a short-sighted policy for there have been great 

 advances in laboratory technique since the material for the Second Edition was 

 assembled in 1947 prior to publication in 1948, which advances should be in- 

 cluded. In fact the advances made, or reported, in the four years 1948, 1949, 

 1950 and 1951 are probably greater than those accomplished in any previous 

 10 year period. Though some of the modifications of standard techniques that 

 proved useful during the war as well as altogether new techniques were published 

 before 1948, many, while known to specialists in various fields, had not been 

 gathered together in convenient form from which laboratory workers as a 

 whole could select those most hkely to be helpful in their particular problems. 

 It is hardly necessary to note that the vast amount of new work in the four years 

 mentioned, reflecting the appreciation of the value of research in medicine 

 and biology gained in the war, and implemented by an unprecedented outpour- 

 ing of funds for research, has resulted in the discovery of new and better means 

 of revealing the structure of organisms from the highest to the lowest in health 

 and disease. The electron microscope has found its way into about 300 labora- 

 tories. Satisfactory methods for cutting the extremely thin sections required 

 have been devised. There is a rapprochement between what one can see at 

 very high magnification and increasing knowledge of molecular structure and 

 orientation determined by several methods. The phase microscope likewise 

 has been produced in quantity in this country. The quality of moving pictures 

 of living cells has thereby been greatly unproved. Thanks to the Atomic 

 Energy Commission radioactive isotopes have been made available. Plastics 

 have been introduced in great variety. Microscopic localization of enzyme 

 activities has been advanced. Microchemistry has leaped ahead. Quantitative 

 analyses of extremely small amounts of material reduce the gap between chem- 

 istry and microscopy. The separation and collection en masse in a condition 

 suitable for analysis of certain cellular components has been most helpful. And 

 so on ahnost without end. 



Obviously no single individual can authoritatively present these new tech- 

 niques, as well as mjTiads of others of great value, because he cannot have 

 personal experience with all of them. Partly to compensate for such limitations 

 I have included descriptions of some of the key techniques written by the in- 

 vestigators who introduced them, or by others who have had extensive experience 

 in their use. Most of these descriptions are new while others are revisions of 

 accounts given in previous editions of this book. The name of each contributor 



