354 POISONS, CONTAGIONS, MIASMS. 



and one grain of the acid to reproduce itself in 

 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 poison 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 transformation was only arrested 

 in consequence of the quantity of oxamide present 

 being limited. In their form both these transfor- 

 mations belong to the same class. But no one but 

 a person quite unaccustomed to view such changes 

 will ascribe them to a vital power, although we 

 admit they correspond remarkably to our common 

 conceptions 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 generation in a definite form. By 

 chemical agency we can produce the constituents of 

 muscular fibre, skin, and hair ; but we can form by 

 their means no organised tissue, no organic cell. 



The production of organs, the co-operation of a 



