LIFE. 151
soon as the living body has begun to change the
composition of the substances upon which it
acts, it endows them with a new set of affinities,
contrary to those which it before possessed
when subject to the operations of chemistry.
Others, again, are content to refer the opera¬
tions in question at once to the ever-ready vital
principle, which, according to them, produces
and directs these changes in the organism, and,
so long as it resides there, keeps in check the
natural tendency of its structure to decay. We
are inclined to believe, on the other hand, that
the operations in question are immediately due
to the agency of the same laws as those which
preside over inorganic matter, operating, how¬
ever, under conditions which the living or¬
ganism alone can supply. We shall now
examine what evidence may be produced in
favour of this opinion, and how far it is con¬
sistent with the general phenomena of life.
V. Changes in composition.—The ali¬
mentary materials which serve as the food of
the living organism, cannot be appropriated by
its several tissues, and rendered like themselves
in structure and properties, until they have un¬
dergone certain changes in composition, by
which the proximate principles are produced.
It is by the organisation of these compounds,
that the constant disintegration of the elemen-
tary parts of the living system is compensated,
and those vital properties maintained, the exer¬
cise of which forms an essential part of the
circle of actions involved in life. Another
class of changes in composition consists in the
production, from the same materials, of the
peculiar ingredients which characterise each se¬
creted product ; some of these may be regarded
as directly eliminated from the nutritious in¬
gredients of the blood, in the same manner as
are the solid tissues themselves ; whilst others
would rather seem to resuk from the new com¬
bination of the disintegrated elements, which
are taken up and removed by the current of the
circulation, and carried to organs destined to
separate them entirely from the living portions
of the system. All these changes are frequently
said to be effected by a vital chemistry ; or (to
speak in more precise language) to result from
the operation of vital affinities, of a different
character from those ordinary chemical affinities
which produce the well-known changes in the
inorganic world. In conformity with the New¬
tonian direction to avoid unnecessarily multi¬
plying causes, we shall briefly examine the
grounds upon which this hypothesis is based,
and enquire whether it is requisite for the ex¬
planation of phenomena, or even gives us any
assistance in our researches.
The chief ground for the assumption of a
distinct set of vital affinities appears to be,
that the mode of union of the elements of the
organic compounds is essentially different from
that which prevails in the inorganic world ;
and that the chemist, who has the power of
effecting or controlling those changes which are
produced by physical laws, and can therefore
imitate to a great extent the immense variety of
combinations which the mineral kingdom af¬
fords, is unable to effect or control the action of
similar materials, so as to produce any of the
class of organic compounds or proximate prin¬
ciples. It has, until very recently, been re¬
garded as a distinctive character of organic
compounds, that their elements are combined
in ternary or quaternary arrangements of com¬
plex nature, in which each ingredient is equally
united with all the rest; whilst all inorganic
substances admit of being ultimately resolved
into simple binary combinations. Thusfibrin
is regarded as composed of 6 parts of carbon,
2 of oxygen, 5 of hydrogen, and 1 of nitrogen ;
and these elements are imagined to form a qua¬
ternary compound, all having a mutual attraction
for each other ; whilst carbonate of ammonia,
which consists of 1 carbon, 2 oxygen, 3 hy¬
drogen, and 1 nitrogen, is a binary combination
of two other binary compounds, carbonic acid
and ammonia. But on this it may be remarked,
that there are undoubtedly some proximate
principles, (that is to say, the simplest forms to
which organic compounds can be reduced,
without altogether disuniting them into their
ultimate elements,) which consist of two ele¬
ments alone, and which exist in this simple
form in living bodies. Such are some of the
compounds of carbon and hydrogen. Further,
the rapid progress of analytic research is leading
to the belief that the complex arrangements
just referred to may be resolved into those of a
binary character; so that most organic com¬
pounds may be regarded as resulting from the
union of others of simpler nature, just as a salt
is formed by the union of an acid and an alkali.
The discovery of cyanogen, and of its capabi¬
lity of acting as a compound radical,—uniting,
like chlorine or iodine, with hydrogen to form
an acid, and even occasionally serving, like
oxygen or sulphur, in combination with some
metals, as the base or alkali to such an acid,—
was the first step in a career of brilliant disco¬
veries, which, even at the present day, may be
regarded as scarcely commenced. When cy¬
anogen combines with a metal, the combination
is in reality a ternary one, although in all its
properties it has a binary character. Thus, the
cyanuret of silver (whose ultimate composition
is 1 part of the metal, with 2 carbon, and 1
nitrogen,) will form a salt, in which it acts as
the acid or negative ingredient, with the cya¬
nuret of potassium; and the soluble cyanurets
will form salts with the chlorides or iodides of
the metals, thus establishing their claim to a
binary character. But still further;—cyanogen
in combination with iron appears itself to act
as a compound radical, combining as a simple
body with other elementary substances* From
the analogy afforded by this and other in¬
stances, many chemists are now disposed to
look upon the combination of the oxy-salts in
a new light. It is suspected that, when sul¬
phuric acid and soda are brought together, the
resulting compound is not formed by the union
of an atom of the acid with an atom of the
alkali, but by the generation of a new com¬
pound radical, sulphatoxygen, consisting of 1
part of sulphur with 4 of oxygen, which unites
* Liebig, in Turner’sLffiemistry, 6th ed. p. 77g.