In preparing this edition, I have done my utmost to correct inaccuracies and remove obscurities. The changes rendered necessary by recent research have also been made.

Some parts have been rewritten ; notably the chapters on the Central Nervous System, to which additional illustrations have been added.

The general arrangement remains the same as that of the First Edition.

I am again deeply indebted to my friend, Mr. E. F. Herroun, for much valuable assistance.

King's College, London.

Preface To The First Edition

The present volume has been written at the desire on the part of the Publishers that a new elementary treatise on Physiology should be added to the series of admirable students' manuals which they had previously issued.

In carrying this desire into execution, I have endeavored to avoid theories which have not borne the test of time, and such details of methods as are unnecessary for junior students. I do not give any history of how our knowledge has grown to its present standpoint; nor do I mention the names of the authorities upon whose writings my statements depend. I have also omitted the mention of exceptional points, because I find that exceptions are more easily remembered than the main facts from which they differ; and, since we must often be content with the retention of the one or the other, I have tried to insure that it shall be the more important.

While endeavoring to save the student from doubtful and erroneous doctrines, I have taken great care not to omit any important facts that are necessary to his acquirement of as clear an idea as possible of the principles of Physiology.

I have not hesitated to lay unwonted stress upon those points which many years' practical experience as a teacher and an examiner has shown me are difficult to grasp and are commonly misunderstood; and I have treated such subjects as are useful in the practice of medicine and surgery more fully than those which are essential only to abstract physiological knowledge.

As medical students are generally obliged to commence the study of Physiology without any anatomical knowledge, I believe it to be absolutely necessary that their first physiological book should contain some account of the structure and relationships of the organs the functions of which they are about to study. I have, therefore, added a short account of the construction of the various parts discussed in each chapter; it has, however, been found necessary to curtail this anatomical portion to a mere introductory sketch. Numerous illustrations, with full descriptions attached to each, are introduced to supplement the explanation given in the text.

So far as is consistent with an accurate treatment of the subject, I have avoided technical terms and scientific modes of expression. I know that in attempting to explain physiological truths in every-day language and in a plain, common-sense way, I run the risk of appearing to lack the precision that such a subject demands; but after mature consideration I have come to the conclusion that great scientific nicety and a scholastic style of expression have a deterrent effect upon the beginner's industry; and I think it is better that he should acquire the first principles of the science in homely language, than pick up technical odds and ends in learned terms the meaning of which he does not comprehend.

As many words strange to the first year's student have to be used, and must be learned, it has been thought advisable to 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 mechanisms 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 commencing with the vegetative systems and following the course of the aliments to their destination and final application, as I believe 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. Tyrrell Brooks for the great help he afforded me by compiling the chapters on Development; 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 skillful manner in which he has executed the new wood-cuts, most of which he had to copy from rough drawings.

King's College, London.