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PREFACE. 
The want of a text-book in the English language to which students 
could turn for information beyond that contained in the ordinary 
manuals has long been felt by teachers of physiology in this country. 
The most extensive of the existing text-books do not aim at giving 
the full and precise information nor the references to original 
authorities which are required by the advanced student. It has 
hitherto been necessary for those who seek such information to consult 
original articles — an operation which frequently involves a familiar 
acquaintance with foreign languages and an expenditure of time rarely 
at the disposal of the student. The present work is not intended 
altogether to supersede this consultation of original papers, but will, 
it is hoped, reduce the need of it to more reasonable limits, and will, 
moreover, by the references to literature which throughout form an 
important feature of each article, facilitate such study where it is still 
necessary. 
A book of this character, from the enormous amount of literary 
labour which is involved in its production, and from the progressive 
character of the science with which it deals, could hardly be undertaken 
by one person. The editor has been fortunate enough to secure the 
co-operation of many of the leading physiologists in this country, each 
of whom deals with some branch of the subject to which he has given 
special attention. Accordingly the reader will find in each article, in 
addition to information as to the present state of knowledge as com- 
plete as it has been possible to make it, many original observations 
upon the matter to which it relates. 
The subjects of generation and reproduction have been omitted in 
this text-book, because, although strictly speaking appertaining to 
physiology, they are studied almost entirely by morphological methods, 
and are more conveniently treated in connection with morphology. It 
has therefore been decided that it would be better not to swell the bulk 
of these volumes, which have already grown beyond the limits originally 
intended, by the introduction of subjects such as these, which possess 
an enormous recent literature, and are exhaustively dealt with in 
special works accessible to every student. The same remark will apply 
to the general physiology of the cell, a branch of biology which has 
