X PREFACE TO THE FOURTH EDITION. 



the following outline of the changes which he has made will show the 

 extent to which this reconstruction has been accomplished : 



Considering it extremely important that his readers should have a 

 clear idea of the sense in which the terms Law and Cause are subse- 

 quently employed, he has devoted a few pages of the Introduction to 

 an explanation of his views upon these points ; and he hopes that he 

 may be there found to have thrown some light upon the philosophy of 

 causation, which may be of assistance to other scientific inquirers. 



In order to make room for a portion of the new matter which he 

 desired to introduce into the treatise, he has felt it necessary to omit all 

 those references to the structure and vital actions of the lower animals 

 which had not an immediate and direct bearing upon Human Physiology ; 

 and consequently, of the First Chapter of the previous editions " On 

 the Place of Man in the Scale of Being," he has only retained so 

 much as related to the characteristics that distinguish Man from the 

 Mammalia which most nearly approach him. The succeeding Chapter, 

 which treated " Of the Different Branches of the Human Family and 

 their Mutual Relations," has been extended in all that relates to Man, 

 and curtailed in that which rather belongs to Comparative Physiology ; 

 and has been transferred to nearly the end of the volume, which the 

 Author considers to be now the more appropriate place for it. 



The Second Chapter of the present Edition, comprising a general 

 view "Of the Chemical Components of the Human Body, and the 

 Changes which they undergo within it," is now for the first time intro- 

 duced. The Author has aimed to render it as complete as its necessary 

 limits would permit; and hopes that he will be found not to have omitted 

 anything truly important, and to have presented a faithful, though con- 

 cise exposition of the present state of our knowledge upon this import- 

 ant subject. In the preparation of this Chapter, he has made great 

 use of the admirable "Physiological Chemistry" of Prof. Lehmann, 

 now in progress of translation by Prof. Day for the Cavendish Society; 

 and not only this, but other portions of his work that involve a scientific 

 knowledge of Organic Chemistry, have had the advantage of Prof. 

 Day's revision a service for which the Author feels greatly indebted, 

 both for himself, and in behalf of his readers. Several new views will 

 be found in this Chapter, which have occurred to the Author during its 

 preparation ; he would especially point to that of the respective rela- 

 tions of Fibrin and Albumen to the nutritive processes, and of the for- 

 mer to the Gelatinous tissues ( 29, 30) ; and to the General Summary 

 which forms the last section, in which the discoveries of M. Cl. Bernard 

 in regard to the elaboration of sugar and fat in the Liver, are placed 

 (he believes) in a somewhat novel aspect. 



