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PREFACE 



IN revising and rewriting this book now for the twelfth time, the aim has been 

 as for all previous editions, to give the student the benefit of the fundamental 

 things which have been worked out in microscopy. The opportunities given by 

 the freedom from teaching have rendered it possible to make this revision more 

 thorough than could be done in any previous edition. 



Progress in all that pertains to microscopy has been marked during the last 

 ten years. Any one can see this clearly by comparing the catalogues of manu- 

 facturers sent out ten years ago with those sent out at the present time. 



Nothing fundamentally new has appeared, but there have been great advances 

 in making practical and usable many processes and much apparatus for which 

 the basic knowledge has existed for a considerable time. Of course there are some, 

 principles and manipulations which a person must become master of if he is to work 

 successfully with the microscope. These have been treated mainly as in the past. 

 Of the new things nothing has been considered in the book which has not been 

 personally tested and found to be workable and helpful. 



Among the most important means recently made available, especially for students 

 of biology, are the following: 



(1) The single objective binocular for all powers of the microscope from the 

 lowest to the highest. 



(2) The dark-field illuminator for all powers, especially the highest powers 

 with which the finest details in living structures can be seen with marvelous clear- 

 ness. This makes it possible to compare the living cell with the fixed and stained 

 one. 



(3) The perfection of apparatus with which the powerful electric lights recently 

 produced have become available for demonstrations and for drawing with the 

 projection microscope. 



(4) The perfection of photographic light filters and the production of dry plates 

 sensitive to the whole spectrum makes it possible to get good photographs of any 

 microscopic specimen, and indeed of any specimen. 



(5) From the numbers who are affected, and the extent of its application, per- 

 haps the greatest improvement of all has been the production of a glass filter which, 

 when used with a gas filled mazda lamp, gives a light of true daylight quality and 

 of sufficient intensity for all powers of the microscope. 



In preparing this edition some parts of the previous edition have been omitted. 

 For example, the pages on micro-chemistry and metallography have been left 



