THE FUNCTIONS OF LIFE. 560 



were demanded, when he again replied with 

 equal readiness, " Without the heat of the sun there 

 could be no life and growth of vegetation" Such 

 is the difference between the unsophisticated 

 common sense of mankind, founded on the daily 

 observation of what is continually passing around 

 us in nature, and the mystic jargon of books filled 

 with metaphysical speculations about "the un- 

 known vital principle" which have tended only 

 to divert the votaries of science from the path 

 that leads to the acquisition of positive and useful 

 knowledge. 



" Some truth there is, but dash'd and brew'd with lies, 

 To please the fools, and puzzle all the wise." 



DRYDEN. 



Corresponding with the facts exhibited in the 

 foregoing tables, the whole organization of birds 

 is more highly developed, and their different 

 functions are performed with greater rapidity, 

 than in mammalia. The stomach is more con- 

 centrated, digestion more vigorous, the heart 

 larger in proportion to their weight, its walls 

 thicker, and its pulsations more frequent. Their 

 blood is more highly organized, or richer in 

 fibrine and red particles, their secretions more 

 copious, and the renewal of their composition by 

 nutrition more rapid. Their bones are harder, 

 their muscles more firm, and their vital power of 

 contraction greater, as shown by the activity of 

 all their movements, and the immense velocity 



