Xll PREFACE. 



tion without appearing to be unimprovable by further inquiry. Physiology 

 is essentially a science of progress; and it must happen that much of 

 what is now regarded as established truth, will need great modification 

 to be brought into accordance with the results of new inquiries. It is 

 very desirable, therefore, that the Student should not be made to think 

 so confidently of his acquirements, as to be indisposed to receive new 

 information, even though it should tend to diminish their value. 



The present Treatise is to be regarded as complete in itself, and as 

 quite independent of the Author's " Principles of General and Compara- 

 tive Physiology." That it may be so he has inserted an introductory 

 chapter on the "Place of Man in the Scale of Being," and numerous 

 references to the Comparative Physiology of the lower Animals. Still 

 he does not hesitate to express the opinion that, the greater the amount 

 of the Student's previous general knowledge of the Science, the better 

 will he be prepared to enter upon any department of it, especially that 

 peculiarly complex and difficult branch, the Physiology of Man. On 

 every topic, it has been the author's aim to present the latest and most 

 satisfactory information within his reach ; and he believes that the Volume 

 contains much that will be new to the Physiologist, whose reading has 

 not been tolerably extensive. Its materials have been but little derived 

 from other Systematic Treatises on the subject ; and it will not be found 

 to bear, as a whole, any considerable resemblance to those already before 

 the public. The author has rather endeavoured to bring together the 

 valuable facts and principles, scattered through the best of the numerous 

 Monographs, that have been recently published on special divisions of 

 Physiology and Medicine ; and to reduce these disjecta membra to that 

 systematic form, w T hich they can only be rightly made to assume, when 

 brought into relation with each other, and shown to be subservient to 

 principles of still higher generality. In regard to this, as to his former 

 Treatise, the Author believes that he may claim a somewhat higher 

 character than that of the mere Compiler ; and that even the well-read 

 Physiologist will find in it many facts and deductions, which have not 

 been previously brought before him in the same form. 



In apportioning the amount of space to be devoted to each division of 

 the subject, the Author has had in view its practical relations, much 

 more than its merely scientific interest; and he has on this account 

 bestowed a much larger share on the organs of Animal life than some 

 may think just when compared with the narrow limits within which other 

 important topics are discussed. But he has endeavoured to keep always 

 in view, that he is writing for the guidance of the Student who is to be- 

 come a Practitioner, rather than for him who makes the pursuit of Science 

 his professed object; and that much that is of the highest interest to the 



