DISTINCTIVE CHARACTERS OF LIVING ORGANISMS. 23 



is recognised by the effects it produces in the same manner 

 as we recognise heat or electricity by their effects may be 

 conveniently designated vital force. 1 Thus, to revert to our 

 previous illustrations, the mechanical power employed in the 

 propulsion of the blood, or in the movements of the limbs, is 

 evolved by muscular contraction, a phenomenon altogether 

 peculiar to the living muscle ; and the muscle derives its pro- 

 perty of contractility from the previous development of its 

 peculiar tissue in the act of nutrition. So the solvent 

 fluids by which the digestion of food is accomplished, are 

 separated from the blood by an act of secretion, which can 

 only be performed by a glandular apparatus in the living 

 walls of the alimentary canal. And the materials for the 

 nutrition of the muscular tissue, and for the secretion of the 

 digestive solvent, as of all the other acts of nutrition and 

 secretion which are continually going on in the living body, are 

 derived from the blood, a liquid which possesses properties 

 very different (as we shall hereafter see) from any mere 

 mixture of chemical compounds, and which is prepared by 

 actions totally beyond the power of the chemist to imitate, 

 the laboratory of the living organism being requisite for their 

 performance. 



6. The whole assemblage of vital actions whiqh is per- 

 formed by the living Animal, may be arranged under two 

 principal groups ; one of them consisting of those which are 

 directly concerned in the development and maintenance of 

 its Organized fabric ; the other including all those by which 

 it is brought into conscious relation with the world around. 

 The former group includes the acts of digestion, absorption, 

 and assimilation, by which the nutritive materials are pre- 

 pared for becoming part of the living fabric ; the circulation 

 of the assimilated materials through the body ; their conver- 

 sion, by the act of nutrition, into the solid textures ; the 

 formation of various secretions, having various purposes to 

 serve in the economy ; the removal, by the acts of respiration 



1 The Author has elsewhere given his reasons for the belief, that 

 Vital force bears the same " correlation " to the Physical and Chemical 

 forces, as the latter bear to each other ; but the discussion of this sub- 

 ject is not suited to an elementary treatise ; and the essential peculiarity 

 of the manifestations of vital force in the phenomena of life, requires 

 that it should be treated as belonging to a distinct category. 



