PREFACE. 



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 stand-point ; 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, 1 nave 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 



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