PREFACE TO THE SECOND EDITION 



Advances in technique have continued. Those Avho would learn about the 

 minute structure of the body in health and disease must have many methods of 

 investigation at their disposal so that they can choose the one most likely to be 

 useful. To be dynamic, their concept of structure must include the organization 

 of living material in space from what can be seen with the naked eye down 

 through that which is microscopically visible to submicroscopic groupings of the 

 smallest particles known to physicists. Consequently brief descriptions of, 

 and leading references to, physical methods capabb of yielding information 

 as to the organization of living material are much in demand. The same can 

 be said for microchemical techniques, because the more accurately investigation 

 of chemical composition, and changes therein, can be focussed on vital structural 

 units the more effective it becomes. Moreover living organisms from the 

 highest to the lowest have many features in common. Techniques of proved 

 value at one level in the scale may well be of use in the investigation of higher or 

 more lowly organisms so that it is well to present them briefly; for otherwise 

 the purpose of this book, to expose in an introductory way the technical oppor- 

 tunities for research, v/hould be limited. For these reasons, and also to include 

 new methods discovered since the first edition was published, as well as im- 

 provements in manj^ standard techniques this book has been considerably 

 expanded. 



As in the case of the First Edition, I am grateful to many of my friends for the 

 frankness of their criticism and their help. This assistance has been given in 

 two principal ways. In numerous cases techniques published in the first edition 

 have been submitted to those who devised them for revision which is acknowl- 

 edged in the text. In other cases investigators have themselves written for 

 me accounts of their own methods, or of groups of techniques in the use of 

 ^vhich they are leaders, which accounts are of course credited to them. Mr. J. M. 

 Albrecht has given very helpful technical advice. Thanks arc due to Miss 

 Margaret Goessling for help in preparing the manuscript. 



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