122 



AGRICULx 



manner, the same decomposition is repeated ; 

 the free oxalic acid enters into combination,, 

 whilst another portion is liberated. In this 

 manner a very minute quantity of oxalic 

 acid may be made to effect the decomposi- 

 tion of several hundred pounds of oxamide; 

 and one grain of the acid to reproduce itself 

 ji unlimited quantity. 



We know that the contact of the virus of 

 small-pox causes such a change in the blood, 

 as gives rise to the reproduction of the poi- 

 son from the constituents of the fluid. This 

 transformation is not arrested until all the 

 particles of the blood which are susceptible 

 of the decomposition have undergone the 

 metamorphosis. We have just seen that 

 the contact of oxalic acid with oxamide 

 caused the production of fresh oxalic acid, 

 which in its turn exercised the same action 

 on a new portion of oxamide. The trans- 

 formation was only arrested in consequence 

 of the quantity of oxamide present being 

 limited. In their form both these transform- 

 ations belong to the same class. But no 

 one except a person quite unaccustomed to 

 view such changes will ascribe them to a 

 vital power, although we admit they cor- 

 respond remarkably to our common concep- 

 tions of life; they are really chemical pro- 

 cesses dependent upon the common chemical 

 forces. 



Our notion of life involves something 

 more than mere reproduction, namely, the ! 

 idea of an active power exercised by virtue ^ 

 of a definite form, and production and gene- j 

 ration in a definite form. By chemical 

 agency we can produce the constituents of j 

 muscular fibre, skin, and hair ; but we can 

 form by their means no organized tissue, no 

 organic cell. 



The production of organs, the co-opera- 

 tion of a system of organs, and their power 

 not only to produce their component parts 

 from the food presented to them, but to 

 generate themselves in their original form 

 and with all their properties, are characters 

 belonging exclusively to organic life, and 

 constitute a form of reproduction indepen- 

 dent of chemical powers. 



The chemical forces are subject to the 

 invisible cause by which this form is pro- 

 duced. Of the existence of this cause itself 

 we are made aware only by the phenomena 

 which it produces. Its laws must be inves- 

 tigated just as we investigate those of the 

 other powers which affect motion and 

 changes in matter. 



The chemical forces are subordinate to 

 this cause of life, just as they are to elec- 

 tricity, heat, mechanical motion, and fric- 

 tion. By the influence of the latter forces, 

 they suffer changes in their direction, an in- 

 crease or diminution of their intensity, or a 

 complete cessation or reversal of their action. 



Such an influence and no other is exer- 

 tised by the vital principle over the chemical 

 forces; but in every case where combination 

 or decomposition takes place, chemical affini- 

 ty and cohesion are in action 



The vital principle is only known to us 

 through the peculiar form of its instruments, 

 that is, through the organs in which it re- 

 sides. Hence, whatever kind of energy a 

 a substance may possess, if it is amorphous 

 and destitute of organs from which the im- 

 pulse, motion or change proceeds, it does 

 not live. Its energy depends in this case on 

 a chemical action. Light, heat, electricity, 

 or other influences may increase, diminish, 

 or arrest this action, but they are not its effi 

 cient cause. 



In the same way the vital principle go- 

 verns the chemical powers in the living body. 

 All those substances to which we apply the 

 general name of food, and all the bodies 

 formed from them in the organism, are che- 

 mical compounds. The vital principle has, 

 therefore, no other resistance to overcome, 

 in order to convert these substances into 

 component parts of the organism, than the 

 chemical powers by which their constituents 

 are held together. If the food possessed 

 life, not merely the chemical forces, but this 

 vitality, would offer resistance to the vital 

 force of the organism it nourished. 



All substances adapted for assimilation 

 are bodies of a very complex constitution ; 

 their atoms are highly complex, and are 

 held together only by a weak chemical 

 action. They are formed by the union 

 of two or more simple compounds; and in 

 proportion as the number of their atoms 

 augments their disposition to enter into new 

 combinations is diminished ; that is, they 

 lose the power of acting chemically upon 

 other bodies. 



Their complex nature, however, renders 

 them more liable to be changed, by the 

 agency of external causes, and thus to suffer 

 decomposition. Any external agency, in 

 many cases even mechanical friction, is 

 sufficient to cause a disturbance in the equi- 

 librium of the attraction of their constitu- 

 ents; they arrange themselves either into 

 new, more simple, and permanent combina- 

 tions, or if a foreign attraction exercise its 

 influence upon it, they arrange themselves 

 in accordance with that attraction. 



The special characters of food, that is, of 

 substances fitted for assimilation, are absence 

 of active chemical properties, and the capa- 

 bility of yielding to transformations. 



The equilibrium in the chemical attrac- 

 tions of the constituents of the food is dis- 

 turbed by the vital principle, as we know it 

 may be by many other causes. But the 

 union of its elements, so as to produce new 

 combinations and forms, indicates the pre- 

 sence of a peculiar mode of attraction, and 

 the existence of a power distinct from all 

 other powers of nature, namely, the vital 

 principle. 



All bodies of simple composition possess 

 a greater or less disposition to form combi- 

 nations. Thus oxalic acid is one of the 

 simplest of the organic acids, while stearic 

 acid is one of the most complex ; and the 

 former is the strongest, the latter one of the 



