ANIMAL. 
But, in addition to these, it is essential, for the 
preservation of their peculiar constitution, that 
they accumulate a much larger portion of nitro- 
gen, and disengage any excess. of hydrogen, and 
especially any superfluity of carbon. This is 
performed by respiration, or breathing, in which 
process the oxygen contained in the atmosphere 
combines with the excess of hydrogen and car- 
bon in the blood; with the former of these, it 
forms watery vapour, and with the latter car- 
bonic acid. The nitrogen, to whatever part of 
the system it may penetrate, seems chiefly, 
though not altogether, to remain there. The 
quantity of nitrogen retained in the system 
varies with the seasons, being greater in sum- 
mer, and less in winter. The degree of varia- 
tion is different for animals of different species : 
| in some it is very small in quantity, while in 
others it is equal to their entire bulk. 
The effects produced upon the atmosphere by 
plants and animals, are of an opposite kind; the 
former decompose water and carbonic acid, while 
| the latter reproduce them. Respiration forms 
the fourth characteristic of animals, and is the 
most distinguishing function of the animal frame; 
| namely, that which forms its essential difference 
from all other beings, and in a manner consti- 
tutes it an animal. So important is its influ- 
ence over the whole body, that we shall presently 
be able to show, that animals perform the func- 
tions of their nature with greater or less perfec- 
tion, according as their respiration is more or 
less perfect. Thus we perceive that animals are 
distinguished from plants by the following char- 
acteristics :—Ist, They are possessed of an intes- 
tinal canal; 2dly, Of a circulating system; 3ddly, 
Nitrogen enters largely into their composition ; 
and, finally, They are endowed with organs 
adapted for respiration. 
To a person who has considered life only in 
man, or in those higher animals which most re- 
semble him, it appears almost superfluous to ex- 
plain the essential difference between an animal 
and a plant. If there existed upon the face of 
the earth only such animals as birds, fishes, or 
quadrupeds, there would then be no occasion to 
enlarge so fully upon the distinctions in their 
functions: the line drawn by the hand of Nature 
would suffice. We should readily be preserved 
from error on this point by their senses, their 
voluntary motion, the symmetry and complexity 
of their structure, but, above all, by the instinct 
which directs their actions. Then we might say 
with Linneeus, “ Vegetabilia crescunt et vivunt ; 
Animalia cresewnt, vivunt et sentiunt” (Vegetables 
grow and live ; Animals grow, live, and feel) ; and 
this definition would be as accurate as it is brief. 
We should not be obliged to separate corals, po- 
lypi, insects, crustacea, and symmetrical shells, 
from the vegetable kingdom. But such is not 
the case. All animals do not exhibit the dis- 
tinctive marks of complicated structure and vol- 
untary motion. This may be easily inferred from 
the fact, that Tournefort, a man of great talents, 
and an able naturalist, actually formed nine gen- 
era in the seventeenth family of his botanical 
system with those polypi which were known to 
him and to his learned contemporaries. At a 
later period, Trembley hesitated for a long time 
before he could determine whether the hydra was 
an animal ora plant; and the experiments which 
he performed to determine the question have been 
admired by all the philosophers of his time. The 
dexterous manipulations of Trembley are the more 
remarkable, as Peyssonel had previously observed 
that minute animals inhabit the different com- 
partments of the corals. This discovery was ex- 
tended by Ellis and Solander to all kinds of poly- 
pi; while Donati, Réaumur, and B. de Jussieu, 
brought the subject prominently forward in their 
public lectures and writings. The question, how- 
ever, still remained in an unsatisfactory state, 
and attracted the attention of the distinguished 
naturalists of the eighteenth century. Buffon 
proposed to establish an intermediate class be- 
tween animalsand plants. Linnzeus adopted this 
suggestion, although it proceeded from Buffon; 
and rendered the distinction permanent by the 
title of zoophytes, or animated plants. The cele- 
brated Pallas followed Linnzeus; Cuvier adopted 
the word and the distinction; while Lamarck re- 
jected them both. These doubts and differences 
of opinion among enlightened men could only 
have proceeded from the obscurity of the subject. 
One cause of the obscurity arose from the false 
direction which their studies had unfortunately 
taken. 
naturalists remained too far from Nature. They 
had found solid bodies—corals, sponges, alcyonia, 
polypi, of innumerable shapes, sometimes covered 
with soft and moveable bodies, and sometimes 
without them. Instead of considering the soft | 
body as the artificer of the solid mass, they be- 
lieved that the latter produced the former; and 
as the solid masses were observed to grow and 
vegetate, they were hastily considered to be plants, 
while the soft bodies were regarded as the flowers 
of these extraordinary vegetables. The error was 
farther confirmed by the circumstance, that at 
the particular period when these polypi repro- 
duce other beings of the same species, their bodies 
are covered with little buds and shoots, which 
bear a great resemblance to certain flowers, the 
structure of which cannot be very distinctly per- 
ceived. But when these supposed flowers were 
observed to be endowed with spontaneous mo- 
tion, and that they were possessed of sensation, 
a great difficulty arose; and the name of zoan- 
thes, or animated flowers, was assigned to them. 
It has now, however, been completely ascertained 
that the polypi themselves fabricate these solid 
apparent vegetables, which serve for their abodes. 
They secrete them in very nearly the same man- 
ner as the mollusca form their shells; the teredo 
its testaceous tube; the lobster its crustaceous 
envelop; the tortoise its shield; the fishes their 
Confining themselves. to their cabinets, | 
