3SO 
the elements of the compound gradually pass from 
an attractive to a repulsive state, by which its original 
constitution is subverted. Thus, when carburetted 
hydrogen or nitrogen, or even carbonic acid, is form- 
ed by seeds placed either in hydrogen, nitrogen, or 
oxygen gas, we see no reason for supposing these 
gases to penetrate the substance of the seed, and, by 
a superior affinity, to draw off its carbon ; but we 
rather suppose this carbon, by a previous change in 
the seed, to be released from its former state of com- 
bination, and brought into a condition more or less 
fitted to combine with the gaseous bodies that sur- 
round it, according to the order of their affinities for 
that substance. 
633. Perhaps the expulsion or emission of carbon, 
under such circumstances, may receive illustration 
from the emission of odorous particles from bodies. 
It will not, we conceive, be said that the emission of 
these particles is caused by the attractive force exert- 
ed by the elements of the atmosphere, but that it 
proceeds from some spontaneous changes going on 
in the body itself, the atmosphere serving only as a ve- 
hicle for the conveyance of these particles, and as a 
medium which readily permits their escape and diffu- 
sion. If, however, these bodies be placed in certain 
circumstances, the emission of their odorous particles 
is more or less checked and prevented. This may be 
accomplished either by withdrawing heat or moisture, 
both of which were necessary to excite and facilitate 
those spontaneous changes on which the emission of 
the odour depended ; or the odour may be arrested 
in its escape by mechanically stopping up the pores 
