PREFACE 



TO 



THE THIRD LONDON EDITION. 



THE Author gladly avails himself of the opportunity afforded him by 

 the call for a Third Edition of the following work, to express his grateful 

 acknowledgments for the kind reception it has experienced, both in this 

 country and in the United States. The rapid sale of two large impres- 

 sions on each side of the Atlantic, has been the most satisfactory proof that 

 he had not been in error when he supposed that an opening existed for 

 an additional Treatise on Physiology, notwithstanding the large number 

 of those already before the public ; and that he has not been altogether 

 unsuccessful in supplying the deficiency. 



The present Edition has not only undergone a very careful revision ; 

 but has in many parts received large additions, and has been in many 

 others entirely remodelled. By an increase in the size of the page, and in 

 the proportion of small type, the quantity of matter has been augmented 

 by an amount equivalent to the addition of fully a hundred pages. A 

 considerable number of new wood engravings, of first rate execution, 

 have also been introduced. Many of these are from original drawings 

 by Mr. Leonard. 



Among the principal additions will be found a Chapter on the Varie- 

 ties of the Human Race ; intended to convey to those, who have not 

 time or opportunity to peruse Dr. Prichard's elaborate treatises, a general 

 view of his arguments and conclusions. The account of the Primary 

 Tissues, also, which was formerly included in the Chapter on Nutrition, 

 has been extended in a degree commensurate with the Author's estimate 

 of its importance, and has been made to form a distinct Chapter nearer 

 the commencement of the work. Other additions and changes, which 

 constitute, when taken collectively, no inconsiderable proportion of the 

 entire Treatise, are scattered through the volume. The materials of 

 these have been drawn from the numerous contributions to Physiological 

 Science, which have been made within the last two years, and from 



