INTRODUCTION. 



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I. DIVISIONS OF THE ANIMAL KINGDOM. 



ALL bodies may, with relation to their modes of existence, 

 be divided into two great classes, the first comprehending 

 those which consist of common matter, subject to the laws 

 of chemical action ; the second comprehending the bodies in 

 which matter is further subject to those other laws to which 

 matter endowed with life is subject. A stone, a metal, or a 

 piece of earth, is common matter, subject to known chemical 

 actions. A plant or an animal is likewise matter, subject to 

 changes of place, or disposition of its constituent particles, by 

 chemical forces. But, while the plant or the animal lives, it 

 is under the influence of other powers, and has its form, ac- 

 tions, and relations, determined and controlled by a distinct 

 system of laws. It is then a living body, and it is only when 

 it ceases to live that it becomes wholly subject to the chemi- 

 cal laws of common matter. 



Of the laws which produce the condition to which we ap- 

 ply the term Life, we know nothing but from certain pheno- 

 mena which the living body presents. The essential cause is 

 amongst those ultimate truths which human reason cannot 

 reach. No approach has been made to solve the mystery of 

 Life ; and at this hour we are as ignorant of the cause of life, 

 and of the agency which connects the powers of mind and 

 the mechanism of the body, as at the first dawning of human 

 inquiry. 



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