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ENZYMES. 39
animal body, undergo within the animal organism a cleavage and oxi-
dation, and yield as final products exactly the above-mentioned chief
components in the nutrition of plants, namely, carbon dioxide, water,
and ammonia derivatives, which are rich in oxygen and have little energy.
The chemical energy, which is partly represented by the free oxygen
and partly stored up in the above-mentioned more complex chemical
compounds, is transformed into other forms of energy, principally heat
and mechanical work. While in the plant we find chiefly reduction
processes and syntheses, which by the introduction of energy from
without produce complex compounds having a greater content of energy,
we find in the animal body the reverse of this, namely, cleavage and oxi-
dation processes, which, as we used to state, convert chemical tension
into living force.
This difference between animals and plants must not be overrated,
nor must we consider that there exists a sharp boundary line between
the two. This is not the case. There are not only lower plants, free
from chlorophyll, which in regard to chemical processes represent inter-
mediate steps between higher plants and animals, but the difference
existing between the higher plants and animals is more of a quantitative
than of a qualitative kind. Plants require oxygen as peremptorily as
do animals. Like the animal, the plant also, in the dark and by means
of those parts which are free from chlorophyll, takes up oxygen and
eliminates carbon dioxide, while in the light the oxidation processes going
on in the green parts are overshadowed or hidden beneath the more intense
reduction processes. As in the animal, Ave also find a heat production
in fermentation produced by plant organisms; and even in a few of the
higher plants—as the aroidcce when bearing fruit—a considerable develop-
ment of heat has been observed. On the other hand, in the animal
organism, besides oxidation and splitting, reduction processes and syn-
theses also take place. The contrast which seemingly exists between
animals and plants consists merely in that in the animal organism the
processes of oxidation and splitting are predominant, while in the plant
chiefly those of reduction and synthesis have thus far been studied.
Wohler l
in 1824 was the first to observe an example of the syn-
thetical processes within the animal organism. He showed that
when benzoic acid is introduced into the stomach, it reappears as hippuric
acid in the urine after combining with glycocoll (aminoacetic acid).
Since the discovery of this synthesis, which may be expressed by the
following equation
:
CoH5.COOH+XH2 .CH2 .COOH = NH(C6H5 .CO).CH2 .COOH+H20,
Benzoic acid Glycocoll Hippuric acid
1
Berzelius, Lehrb. d. Chemie, iibersetzt von Wohler, 4, p. 356, Abt. 1, Dresden
(1831).
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