PREFACE TO THE FOURTH EDITION. XI 



From the consideration of .the chemical components of the organism, 

 and of the participation of chemical forces in its operations, it seemed 

 natural to pass on to that of " The Structural Elements of the Human 

 Body, and the Vital Actions which they exhibit," which forms the sub- 

 ject of the Third Chapter. Nearly the whole of this Chapter, which 

 includes the general doctrines of Cell-formation and of Vital Force, in 

 their application to Human Physiology, appears for the first time in 

 this edition. 



Passing on to the more detailed survey of the constituent parts of the 

 Human body, the first place seemed to be claimed by the Blood; the 

 "Physical Characters, Chemical Composition, and Vital Properties" of 

 which are treated of at some length in Chapter IV. This portion has 

 been greatly extended, and almost entirely rewritten ; the great import- 

 ance of the subject, in its bearings on Pathology as well as on Physio- 

 logy, having been constantly kept in view. The Author does not profess 

 to have included by any means all that might have been brought together 

 on the subject ; but he has selected those facts with which he considered 

 it most important that his readers should be acquainted, and those doc- 

 trines which seemed to him to have the most direct practical applications. 

 As original contributions to this department of Physiology, he would 

 especially point to the correction ( 154) of the ordinary analyses of the 

 Blood (the essential point of which, he may remark, has been brought 

 under the notice of the French Academy by M. Lecanu, some months 

 since this chapter passed through the press); and to the account of that 

 state of the blood which gives a special predisposition to zymotic dis- 

 ease ( 210) a doctrine, which, although to a certain extent hypothe- 

 tical, will be found (he believes) to be in such strict accordance with all 

 the known facts bearing upon the subject, as to be almost entitled to 

 rank as a legitimate generalization of them. 



The Fifth Chapter, " On the Primary Tissues of the Living Body; 

 their Structure, Composition, and Actions," is essentially the same with 

 the Third Chapter of the previous Edition ; but a large amount of new 

 matter, in great part supplied by the elaborate " Mikroscopische Ana- 

 tomie" of Prof. Kblliker, has been incorporated in it; and many new 

 illustrations, chiefly derived from the same source, have been introduced. 

 The account of the vital endowments of the Muscular and Nervous tis- 

 sues, previously contained in other chapters, has been transferred to 

 this ; so as to make it embody a complete sketch of those physiological 

 actions of the separate parts of the organism, which are afterwards to 

 be considered in their relations to each other. 



This Chapter is followed, as in the previous Edition, by a " General 



