PREFACE. 



The historical portion of this volume has been condensed 

 from notes made from time to time in the study of the 

 subject. With the view of making it as short as possible, 

 I have given only those experiments and observations that 

 seemed important to a proper understanding of the subject, 

 avoiding all but the most necessary details; aiming at the 

 same time to preserve all that will be of real advantage to the 

 general student. Many familiar names will be missed, for 

 the reason that many have written, and some of them very 

 well indeed, who have developed no distinctive fact or 

 thought that is of service in the farther progress of the sub- 

 ject. When we come to analyze any such subject, most men 

 are surprised to find how few have been instrumental in the 

 development of the real basic facts on which our knowledge 

 of it rests. Therefore, if we can properly estimate the import 

 of the matter presented, the history of the development of 

 any such subject may be briefly written. Whether or not I 

 have determined wisely, the intelligent reader must judge. 



The second part was written because I had something to 

 say that I thought ought to be said at the present time. The 

 men who have been most instrumental in the development of 

 this subject have given us little else than the experimental 

 facts. These will satisfy the minds of but very few. Most 

 of us appreciate any subject more if we understand why these 

 things are so. It is this why that I have sought to supply. 

 This I leave for intelligent discussion to sift, and separate the 

 good grains from the chaff. 



G. V. BLACK, M. D., D. D. S. 



JACKSONVILLE, June 2d, 1884. 



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