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 which 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. 
