PREFACE. 7 



of proximate principles are by far the most important to us as 

 physiologists, these have been specially dwelt upon, and 

 their relations to nutrition followed out as completely as 

 possible, with our present knowledge. A consideration of 

 the excrementitious proximate principles, being connected 

 exclusively with excretion, has been deferred, to be taken up 

 in connection with that function. 



In treating of physiology proper, it has been the design 

 of the author to present what is actually known regarding 

 the functions of the body ; and in order to facilitate their 

 study, he has generally commenced the consideration of in- 

 dividual functions with a sketch of the physiological anat- 

 omy of the parts. This is the natural point of departure in 

 the thorough investigation of any special function. 



The science of physiology dates from the earliest periods 

 in the history of medicine; and certain important physio- 

 logical facts were demonstrated experimentally hundreds of 

 years ago. While the author has regarded purely historical 

 considerations, and discussions of mere theoretical questions, 

 as unprofitable, he has attempted to give due credit to those 

 who, by their experiments and observations, have contributed 

 to bring the- science to its present condition. "With this view, 

 he has procured and consulted, as far as possible, accounts of 

 original investigations ; but from the poverty in physiologi- 

 cal works of the public libraries to which he has had access, 

 it has been necessary to depend to a certain extent on the 

 exhaustive treatises on physiology published in other coun- 

 tries. Though, undoubtedly, he has been unable in all in- 

 stances to give due credit to every observer, this has been 

 attempted as far as possible. 



It is an undoubted fact that nearly all the important 



