PREFACE TO THE SECOND EDITION. 



Two years ago the first edition of this work was published. Since 

 that time several thousand copies have been disposed of; it has been in- 

 troduced as a text-book in many of our medical schools, and has been 

 very favorably received by the profession and the public. 



I have therefore felt it necessary to submit it to a careful examination, 

 for the purpose of removing any errors it may contain, and improving it 

 as far as its present form admits. The revision it has undergone will, I 

 hope, make it worthy of the continued patronage of those who have hith- 

 erto shown it so much encouragement. 



In these corrections I have availed myself of many of the suggestions 

 made in various reviews of the original work, and take this occasion to 

 express my thanks for the consideration shown toward it both in Amer- 

 ica and Europe. JSTo one knew better than myself how numerous were 

 its imperfections. The manner in which they have been overlooked has 

 served to convince me that those who were judges of the science, and 

 could deal authoritatively with it, were disposed to encourage any at- 

 tempt at its improvement, even though that attempt was marked by 

 many conspicuous shortcomings. 



For doubtless they saw that this book aimed at much more than was 

 directly expressed upon its pages. To- treat Physiology as a branch of 

 Physical Science ; to exclude from it all purely speculative doctrines and 

 ideas, the relics of a philosophy (if such it can be called) which flourished 

 in the Middle Ages, though now fast dying out, and from which the more 

 advanced subjects of human knowledge, such as Astronomy and Chem- 

 istry, have long ago made themselves free to do this, amounts, in reality, 

 to a reorganization and reconstruction : a task of extreme difficulty, and 

 for complete success demanding the conjoint labors of many philosophers 

 and many physicians. 



At the best, therefore, such an attempt, embracing the whole science, 

 made by a single individual, must needs be unsatisfactory, if any thing 

 like a rigorous criticism be applied. And yet it may be truly said that 

 the interest of the medical profession at the present time requires that 

 such encouragement as this work has received should be extended to 

 every undertaking of the kind. I hope that the success which has in 



