INTRODUCTION. 



THIS work was begun about three years ago, under the conviction that 

 much remained to be accomplished in illustrating, by photography, the 

 structure of the central nervous system. After experimenting with va- 

 rious methods, I found that satisfactory prints could be made, in ink, 

 directly upon plate paper, and that these impressions were as perfect in 

 fine detail as any of those obtained by the silver process of printing. 



The plates, which form the larger part of the book, are as durable 

 as steel engravings, and have all been printed by the artotype process, 

 from my own negatives of sections selected from over five thousand 

 preparations made by my own hands. This will in part account for the 

 time spent, the difficulty of making and mounting sections, suitable for 

 good photography, being well known. 



Last year, I distributed several incomplete sets of mounted and 

 varnished prints from some of the same negatives ; and the writers of the 

 very flattering acknowledgments,which I have received, are in no small 

 measure responsible for the present publication. 



My thanks are especially due to Dr. J. J. Woodward, for indispen- 

 sable assistance at the very commencement of my work, in practically 

 explaining his method and theory of illumination of the object, and for 

 advice and encouragement on several occasions. 



Without the valuable help of Prof. S. F. Baird, and the Smith- 

 sonian Institution, many of the most important illustrations could not 

 have appeared for several years. 



