6 PREFACE. 



pure human physiology, and will embrace physiological 

 chemistry and the anatomy of the tissues and organs of the 

 body, only so far as necessary for the elucidation of the func- 

 tions of the organism. Though, undoubtedly, the chemistry 

 and general anatomy of the tissues and organs strictly belong 

 to physiology, they present many points which have no bear- 

 ing, that we are as yet able to comprehend, upon the func- 

 tions. In the present condition of the science, a considera- 

 tion of these would only encumber and obscure the history 

 of the physiological processes. While it is undoubtedly true 

 that every advance in physiological chemistry or histology 

 will have its bearing, sooner or later, upon physiology, it is 

 evident that discoveries in these departments must be multi- 

 plied and coordinated before their relations to the functions 

 can be fully appreciated. Until then they are specially inter- 

 esting only in a chemical and anatomical point of view. In 

 the same way every discovery in physiology, no matter how 

 unimportant it may at first appear in a practical point of 

 view, will eventually have its bearing upon practical medi- 

 cine, surgery, or obstetrics ; yet it will not find its way into 

 works on those subjects until its relations become apparent. 



As an introduction to the study of physiology proper, a 

 certain amount of knowledge of physiological chemistry is 

 indispensable. It is in this direction that we are to look for 

 advances which will enable us to comprehend the processes 

 of nutrition, the end and object of all the vegetative functions 

 of the body. The introduction, then, is devoted to physiolog- 

 ical chemistry. No attempt has been made to treat of this 

 subject exhaustively, or to include a consideration of all the 

 proximate principles which have been isolated and studied. 

 As the general properties and relations of the different classes 



