PREFACE. 



O IXCE the last edition of this work, nearly all the departments of 

 medicine have been cultivated with marked success; and the ad- 

 vances in physiological science during that time have made it desirable 

 to revise the greater part of the book, and, in some respects, to modify 

 its arrangement. In the section of Physiological Chemistry, the most 

 important alterations relate to the classification of the Albumenoid 

 Substances, and particularly to the prominence given to the Ferments 

 as a special group. Although we are still very imperfectly acquainted 

 with the chemical constitution of these bodies, and are even able to 

 recognize them rather by the effects which they produce than by their 

 physical properties, yet their physiological activity has assumed an im- 

 portance which makes it necessary to consider them by. themselves. In 

 treatises exclusively devoted to Physiological Chemistry, the albumenoid 

 substances are usually classified according to their characters of solu- 

 bility in neutral, acid, or alkaline media, or in saline solutions of dif- 

 ferent degrees of concentration, or by the varying conditions of their 

 coagulability ; but in a work like the present, an arrangement based on 

 their physiological properties and destination is both more useful and 

 more intelligible. The same remark will apply, in great measure, to 

 the other principal groups of organic substances. 



In the department of the Xervous System, more extended considera- 

 tion has been given to the localization of function in special parts of the 

 cerebro-spinal axis. The recent progress of investigation in this respect 

 relates not only to the cerebral convolutions and their connection with 

 various forms of movement and sensation, but also to the identification 

 of special communicating tracts of white substance in the brain and 

 spinal cord. The general use of hardened and stained preparations, and 

 improved methods in making microscopic sections, have largely increased 

 our knowledge of the intimate structure of the nervous centres; and 



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