PREFACE. lx 



add a short glossary, containing an explanation of the most 

 ordinary physiological expressions. 



Great difficulty is always found in fixing upon a starting 

 point at which to begin the study of Physiology. To begin 

 with the circulation of the blood, which is so essential for the 

 life of every tissue, one should have some knowledge of nerve 

 and muscle. To begin with nerves and muscles the mechan- 

 isms and the uses of the blood current should be understood ; 

 and so on throughout the various systems, which are so inter- 

 dependent that, for the thorough comprehension of any one, a 

 knowledge of all is required. 



I have, therefore, adopted the time-honored plan of com- 

 mencing with the vegetative systems and following the course 

 of the aliments to their destination and final application, as I 

 believe that this arrangement is open to as few objections as 

 any other known to me. 



I wish here to express my most cordial thanks to many 

 friends who have aided me with kind assistance and advice. 

 I am deeply indebted to Mr. W. Tyrrell Brooks for the great 

 help he afforded me by compiling the chapters on Develop- 

 ment; and I feel I cannot sufficiently thank Mr. E. F. Herroun 

 for his untiring and valuable assistance in the revision of the 

 proof-sheets. 



To Mr. G. Hanlon I am indebted for the careful and skilful 

 manner in which he has executed the new woodcuts, most of 

 which he had to copy from my rough drawings. 



KING'S COLLEGE, LONDON, January, 1884. 



