OF VITAL MOTION. 47 



induce an undue and partial expansion in certain 

 vascular tubes, and then suppose as the consequence 

 of this an increased afflux of blood, which again, by its 

 own peculiar molecular changes, would keep up and 



servient to the wants of the animal system, for to animal and 

 vegetable it is a direct and deadly poison. We are obliged to 

 admit, therefore, that inorganic bodies are concerned in the 

 decomposition of this gas for agents must be employed to 

 conquer the affinities of its component elements; and as this is 

 the case here, so also we may argue, in relation to carbonic 

 acid, that inorganic bodies under the influence of light are 

 endowed with a similar depuratory office. 



As to the identical bodies which may he concerned in the 

 removal of carbonic acid and other poisonous gases from the 

 atmosphere, we may infer, from the history of spongy platinum, 

 that these are the porous rocks and earths. We know that the 

 peculiar properties of the metal are chiefly owing to the infinite 

 extension of surface by which the substance to be acted upon 

 is brought into intimate contact "with the agent, and there- 

 fore a similar property may, without any improbability, be 

 claimed for other mineral bodies in which this condition exists. 

 And hence we may see new proofs of design and beauty in the 

 world around us. The porous rocks, when lighted by the sun- 

 beams, may be intended to filter and purify the air as well as the 

 waters, and so made to serve a purpose which could not be 

 answered by crystalline solids like marble or granite. The belt 

 of sand which encircles the sea may also have a similar office, 

 and the activity of its several particles be increased perhaps by 

 the continual washings of the tides. And, finally, the bound- 

 less deserts of torrid climes may have some relation to the 

 exuberant life of other parts of the same regions, and instead of 

 being wild and dreary desolations, they may be important means 

 by which the atmosphere is purified, and health secured to man, 

 and beast, and plant. 



