VI 4 PREFACE. 



On the whole subject of physiology proper, as it applies to the func- 

 tions executed by the different organs, the present edition, the author 

 natters himself, will be found to contain the views of the most distin- 

 guished physiologists of all periods. The contributions to the science 

 of life have, of late years, been rich and varied ; and to collate and 

 weigh them, and to separate the most trustworthy and valued, has been 

 a work of no little discriminating labour, but to the author a labour 

 of Jove, inasmuch as they are subjects which he has been long accus- 

 tomed to investigate : and on which he has annually to treat before the 

 class of Institutes of Medicine of the Jefferson Medical College. The 

 Bibliography, prefixed to the first volume, will exhibit the number 

 and variety of sources of information at home and abroad, which he 

 has had to consult, and will afford a coup d'oeil of the chief biological 

 investigations, undertaken since the appearance of the last edition more 

 especially, which have so changed the face of the science in regard to 

 certain subjects as to require that they should be re-written. 



The rich collection of materials in the possession of his publishers 

 has enabled him to increase greatly the list of illustrations, and to 

 substitute in 'many cases better; whilst new cuts have been added so 

 as to make the whole number four hundred and seventy-four, in place 

 of three hundred and sixty-eight, as in the last edition. It has been 

 difficult in all cases to assign these to the original projectors ; but an 

 effort has been made so to do. 



On no former occasion has the author felt as satisfied with his endea- 

 vours to have the work on a level with the existing state of the science ; 

 and, for the seventh time, he ventures to place it before a profession, 

 which has already done too much honor to his efforts to be useful. 

 His crowning desire, in all his literary undertakings, has been to faci- 

 litate the onward course of those who are pressing forward to distinction 

 in a truly learned and difficult profession, and the reception these un- 

 dertakings have met with has satisfied him, that his labours have been 

 far from fruitless. 



EOBLEY DUNGLISON. 



18 GIBARD STREET, 



August, 1850. 



