NATURE AND CONDITIONS OF LIFE. I I 



The more philosophical view, then, as to the nature of 

 the connection between life and its material basis, is the one 

 which regards vitality as something superadded and foreign 

 to the matter by which vital phenomena are manifested. 

 Protoplasm is essential as the physical medium through 

 which vital action may be manifested ; just as a conductor 

 is essential to the manifestation of electric phenomena, or 

 just as a paint-brush and colours are essential to the artist. 

 Because metal conducts the electric current, and renders it 

 perceptible to our senses, no one thinks of therefore assert- 

 ing that electricity is one of the inherent properties of a 

 metal, any more than one would feel inclined to assert that 

 the power of painting was inherent in the earners hair or in 

 the dead pigments. Behind the material substratum, in all 

 cases, is the active and living force ; and we have no right 

 to assume that the force ceases to exist when its physical 

 basis is removed, though it is no longer perceptible to our 

 senses. It is, on the contrary, quite conceivable theoreti- 

 cally that the vital forces of an organism should suffer no 

 change by the destruction of the physical basis, just as elec- 

 tricity would continue to subsist in a world composed uni- 

 versally of non-conductors. In neither case could the force 

 manifest its presence, or be brought into any perceptible 

 relation with the outer world; but in neither case should we 

 have the smallest ground for assuming that the power was 

 necessarily non-extant. 



b. Organisation. Having decided that the presence of a 

 certain physical basis or peculiar form of matter is essential to 

 the manifestation of vital phenomena, we may next pass on to 

 consider whether organisation, or the presence of a certain de- 

 finite structure, is one of the essential conditions of vitality. 

 It is a very common thing to speak of animals as if they were 

 so many machines, and from one limited point of view the 

 comparison is a fair and useful one. Eveiy machine, however 

 simple, is composed of certain definite parts which have cer- 

 tain definite relations to one another; and every machine, 



