144 OF THE STRUCTURAL ELEMENTS OF THE HUMAN BODY. 



turn may become the instrument of a similar metamorphosis. And we have 

 the same kind of evidence, that Light and Heat, acting upon the organic germ, 

 become transformed into Vital force, which we possess of the conversion of Heat 

 into Electricity by acting on a certain combination of Metals, or of Electricity 

 into Magnetism by being passed round a bar of iron, or of Heat or Electricity 

 into Motion when their self-repulsive action separates the particles of matter 

 from each other. For we shall presently find, that just as Heat, Light, Chemi- 

 cal Affinity, &c., are transformable into Vital force, so is Vital force capable of 

 manifesting itself in the production of Light, Heat, Electricity, Chemical Affinity, 

 or Mechanical Motion ; thus completing the proof of that mutual relationship, 

 or " correlation, " which has been shown to exist among the Physical and Che- 

 mical forces themselves. 



125. In order, however, to arrive at a definite and complete conception of the 

 source of Vital force in the Human Organism, it will be necessary to examine, 

 a little more in detail, into the reciprocal relations, material and dynamical, 

 which subsist between the Animal and Vegetable kingdoms, and between these 

 and the Inorganic world. The Plant, when acted on by Light, forms certain 

 organic compounds, at the expense of the water, carbonic acid, and ammonia, 

 of the soil and atmosphere, decomposing these binary compounds into their four 

 elements, and uniting these again into ternary and quaternary combinations of 

 a very peculiar character } and the Light, by whose agency alone this process 

 can be effected, may be considered as metamorphosed into the peculiar affinity, 

 or chemical force, by which the elements of these compounds are held together. 1 

 The pabulum thus generated is applied by the Vegetable organism to the exten- 

 sion of its own structure, the vital force requisite for this purpose being sus- 

 tained by Heat acting ab externo ; and thus the fabric may be augmented to an 

 almost unlimited extent, every increase of surface affording a new instrument 

 for the agency of light, and thus affording the conditions requisite for the pro- 

 duction of an additional amount of organic compounds. The whole nisus of 

 vegetable life may be considered as manifesting itself in this production ; and, 

 in effecting it, each organism is not only drawing material, but force from the 

 universe around it. Supposing that no Animals existed to consume these or- 

 ganic compounds, they would be all at last restored back to the inorganic con- 

 dition by spontaneous decay, which would reproduce the water, carbonic acid, 

 and ammonia, from which they were at first generated. In this decay, how- 

 ver slow, light and heat would be given out, in the same amount as when more 

 evidently produced in the ordinary combustive process ; and we do in fact ob- 

 serve, that, during certain phases of vegetation (namely, germination and flow- 

 ering) a sensible amount of Heat is produced by many plants as one of the 

 ordinary phenomena of their lives, Light also being occasionally manifested. 3 

 Moreover, spontaneous movements are sometimes to be observed in Plants, 

 under circumstances which indicate that they are to be considered as manifesta- 

 tions or expressions of Vital force; and thus the Vegetable, even during its 

 life, may restore to the Universe some portion of the forces which it has derived 

 from it under other forms. It is only, however, when the complete conversion 

 of the organic compounds it has formed, into the binary compounds which fur- 

 nished their materials, has taken place, that the Plant can be considered as hav- 

 ing wholly given back the forces which it consumed in their first production; 

 and this period may be also indefinitely postpoaed by the preservation of these 

 substances ; so that in fact it is only now, that Man, whilst consuming the 



1 That Light, or some component of it, ceases to exist as such, when it thus operates 

 upon living Vegetable surfaces, is shown by the curious fact that such surfaces are al- 

 ways represented in Photographic pictures as if they were black, that is, as if they received 

 or reflected no light at all. 



2 See "Prin. of Phys., Gen. and Comp.," \\ 607, 616, Am. Ed. 



