LECTURE III. 



On the Study of Physiology. — The Aids and Illustrations to be 

 derived from other Sciences ; as, Natural Philosophy, Mathe- 

 matics, Chemistry. — Study of the Physical Sciences recommended. 

 — Peculiar Character of the Vital Phenomena — Living Pro- 

 perties — Attempted Hypothetical Explanations of them. — Com- 

 parative Anatomy — its Objects — its Relations to Physiology 

 exemplified. 



Dissection, and the various auxiliary processes employed 

 by the anatomist, are the only means of learning the struc- 

 ture of living beings ; — observation and experiment, the 

 only sources of our knowledge of life. These are the tests, 

 or criteria, on which we must depend, and to which we 

 must always refer. No position respecting structure can be 

 listened to, unless it admits of verification by ai3peal to 

 anatomy ; no physiological statement deserves attention, 

 unless it be confirmed by observation. 



Is this then all ? Are the labours of so many celebrated 

 men, the accumulated harvests of so many centuries, re- 

 duced to the mere results of dissection and observation ? It 

 is so, in respect to real knowledge ; and it will be occupa- 

 tion enough to anatomists and physiologists, for many ages, 

 to cultivate these pursuits. The multitude and variety of 

 organs in the human body, the complexity of their struc- 

 ture, the modifications incidental to each, and their mutual 

 influences, offer a most extensive field of investigation ; re- 

 quiring so much time and assiduity, so much caution and 

 discrimination, that the qualities necessary to a successful 

 pursuit of physiology cannot be often combined in one in- 

 dividual. 



When to man we add all the living beings which fill 

 every department of nature, and consider the diversities 



