476 THE DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 
evolution of oxygen. But this process occurs only in plants ex¬ 
posed to sun-light, and seems rather to be analogous to the diges¬ 
tion in animals; and we believe the true functions of respiration in 
plants to consist, as in animals, of an absorption of oxygen and 
evolution of carbonic acid, and this process we know takes place 
both by night and day in plants. 
Generally speaking, animal structures are quaternary com¬ 
pounds, consisting of carbon, oxygen, hydrogen, and nitrogen; 
whereas vegetable structures are usually ternary compounds, being 
composed of carbon, oxygen, and hydrogen ; but there are many 
instances of plants possessing nitrogen as a component part of 
their structure, as, for instance, the cruciferca and fungi. 
Another distinctive character between animals and plants is 
derived from the nature of their food; the food of plants con¬ 
sisting of elements derived from the inorganic kingdom, which 
they convert into certain organic compounds, while the food of 
animals is derived from the organic kingdom. Animals do not 
possess the power of converting inorganic materials into the sub¬ 
stance of their tissues, hence they are dependent upon plants for 
their means of support; and here we may notice the beautiful 
provision of Nature, by which one kingdom is made subservient to 
the uses of the other. 
We see, therefore, that in the present state of science we cannot 
draw a distinct line of demarcation between the two kingdoms. 
Numerous tables of supposed distinctive characters have been 
drawn up, of which the following has been given by Dumas:— 
PLANTS 
Produce indifferent substances con¬ 
taining nitrogen ; 
- fats; 
- several varieties of sugar, 
starch, and gum. 
Decompose carbonic acid; 
--- water; 
-ammoniacal salts. 
Give off oxygen. 
Absorb warmth ; 
- electricity. 
Are apparatus of reduction. 
Are immoveable. 
ANIMALS 
Consume indifferent substances con 
taining nitrogen ; 
-fats; 
-sugar, starch, and gum. 
Produce carbonic acid ; 
- water ; 
- ammoniacal salts. 
Absorb oxygen. 
Produce warmth ; 
- electricity. 
Are apparatus of oxidation. 
Change their place. 
We have already shewn that several of these characters will 
not bear the test of examination, and we might also proceed to point 
out many exceptions to all the remainder; but sufficient has been 
already stated to prove, that, in estimating the distinctions between 
the two kingdoms, we must be satisfied with characters taken from 
entire kingdoms, rather than from individuals; and then we shall 
