4 
REVIEW OF CERTAIN DOCTRINES 
ability of water in the one case to prevent, in the other to 
promote absorption of oxygen. 
An electric spark, or any ignited body, a wire made in- * 
candescent by a galvanic discharge, has an influence ana- 
logous to platina sponge, of which the minutest particle is 
sufficient to cause ignition throughout an inflammable mix- 
ture, however large. There is, in this respect, an analogy 
between the explosion of inflammable, gaseous mixtures, 
and those of gunpowder, and of other fulminating powders, 
of which some, as it is well known, detonate by percussion 
or friction, or any cause adequate to derange the equili- 
brium of their particles. In the cases last mentioned, the 
change produced is the same, whatever may be the exciting 
cause, and the minutest portion of the congeries being made 
to undergo the change, is of itself competent to produce a 
like result as respects the whole. 
Evidently the property which bioxide of hydrogen, and the 
oxide of silver, or bioxide of lead, have, of* undergoing an ex- 
plosive deoxidizement in consequence of mere superficial con- 
tact, is in some respects peculiar, since the reaction is recipro- 
cal. In the solution of the alloy of platina with silver, one 
body induces another to undergo the oxidizement to which 
it is itself subjected. In the case of the bioxide of hydro- 
gen and oxide of silver, two bodies, both prone to de-oxl- 
dizement, reciprocally induce that species of change. Be- 
sides, in this phenomenon, there is no third body to perform 
a part analogous to that of the nitric acid. From both of 
the two last mentioned instances, that of platina sponge dif- 
fers, inasmuch as it undergoes no change, during its cata- 
lytic agency. 
Not only have ferments power to produce a change, but 
also severally to produce the particular change by which 
either sugar, alcohol, acetic or lactic acid, &c, &c, is 
respectively generated. Moreover, these bodies are them- 
selves meanwhile undergoing an oxidation or decomposi- 
tion which is necessary to their power; but the change thus 
