AUTHOR'S PREFACE. 



SINCE the publication of the first edition of this work, Che- 

 mistry and more especially Physiological Chemistry has been 

 so zealously and extensively cultivated, and has been enriched by 

 the acquisition of so large a mass of new facts and discoveries, that 

 we may regard the last ten years as one of the most important 

 periods in the history of this science. Hence a simple enlarge- 

 ment of the earlier edition would not have enabled us to consider 

 all the advances made within this short period, which rather 

 required that the whole work should be entirely remodelled, both 

 in relation to its form and contents. The most superficial compa- 

 rison of the two editions will suffice to show that this volume has 

 been subjected to so entirely new a mode of arrangement, that only 

 a few paragraphs have been borrowed from the earlier edition ; for 

 thus alone could a faithful representation of the present state of 

 this department of chemistry be afforded. 



The rapid advance of science and the extraordinary accumu- 

 lation of a mass of crude materials, some of which may not even 

 be capable of acquiring form, must plead in extenuation of the 

 delay that has attended the publication of the second volume. 

 There are, however, two causes which render this delay in some 

 degree pardonable. The one depends upon the intimate connexion 

 of the objects under consideration with histology, the history of 

 development, and pathological anatomy ; and as the censure, 

 which has more or less justly been thrown on the writers on 

 physiological chemistry, may be traced to ignorance or neglect 

 of the kindred branches of science, the author has endeavoured 

 to fit himself for the task of critically reviewing the labours of 

 others, by acquainting himself, through personal observation and 

 experience, with the grounds on which these departments of 

 science are based. The great mass of voluminous and often 



