6 
OllGANIC FORMS OF THE ANIMAL BODY. 
organs for circulating their fluids, being the second characteristic peculiar 
to animals. It is not so essential, however, as the digestive system, for it 
is not found in the more simple species. 
The complicated functions of animals require organized systems, which 
would be superfluous in vegetables ; such as, the muscular system for vo- 
luntary motion, and the nerves for sensation. It was also necessarj' that 
the fluids should be more numerous and varied in animals, and possessed 
of a more complicated chemical composition than in plants, in order to 
facilitate the action of these two systematic arrangements. Therefore, 
anotiier essential element was introduced into the composition of animals, 
of which plants, excepting some few tribes, are generally deprived ; and 
while plants usually contain only three elements, oxygen, hydrogen, and 
carbon, animals add to these a fourth, namely, azote or nitrogen. This 
difference in chemical composition forms the third trait in the character 
of animals. 
Plants derive their nourishment from the soil and atmosphere, and thence 
obtain water, composed of oxygen and hydrogen ; also, carbonic acid, 
which is a compound of carbon and ox 5 gcn ; while the atmosphere yields 
an unlimited supply of air, composed of oxygen and nitrogen [with a slight 
mixture of carbonic acid.] From these materials, the supplies necessary 
to preserve their own composition unaltered, are obtained; and, while 
hydrogen and carbon [with a certain portion of oxygen] are retained, 
they exhale the superfluous oxygen [untainted.] The nitrogen, on the 
contrary, is [either absorbed in very small quantities, or] altogether re- 
jected. Such is the theory of vegetable composition ; in which one of 
the most essential parts of the process, namely, the exhalation of o.xygen, 
can only be performed by the assistance of light. 
When plants are deprived of light, an opposite effect ensues. Instead of giving 
off- oxygen-gas, and absorbing carbonic acid, the reverse takes place ; and carbonic acid 
is disengaged, while oxygen is absorbed. The effect of plants upon the air is, there- 
fore, to increase its purity during day-light, but to deteriorate its quality during the 
darkness of night. 
Animals require for their nutriment, directly or Indirectly, the same 
substances which enter into the composition of vegetables, namely, hy- 
drogen, carbon, [and a certain portion of oxygen.] But, in addition to 
these, it is essential, for the preservation of their peculiar constitution, 
that they accumulate a much larger portion of nitrogen, and disengage 
any excess of hydrogen, and especially any superfluity of carbon. This 
is performed by respiration, or breathing, in wliich process the oxygen 
contained in the atmosphere combines with the [excess of] hydrogen 
and carbon in the blood ; with the former of these, it forms watery va- 
pour, and with the latter carbonic 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 siunmer, and less in winter. The degree of variation is different for ani- 
mals of different species: in some it is very small in qua:itity, 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 character- 
istic 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 constitutes it an animal. So important is its influence 
over the whole body, that We shall presently be able to show, that ani- 
mals perform the functions of their nature with greater or less perfection, 
according as their respiration is more or less perfect. 
Thus we perceive that animals arc distinguished from plants by the following cha- 
racteristics : — 1st, They are possessed of an intestinal canal; 2dly, Of a circulating 
system; 3dly, Nitrogen enters l.wgely into their composition; and finally. They are 
endowed with organs adapted for respiration. 
SECT. IV. THE ORGANIC FORMS OF THE ANIMAL EODY, AND THE PRINCIPAL 
CHEMICAL ELEMENTS OP ITS COMPOSITION. 
Cellular Tissue 'feinbranes — Gelatine — Medullary Substance — Muscular Fibre — 
Pihrin Blood. Albumen — Secretion — Nutrition. 
A POROUS tissue of network, and at least three chemical elements (car- 
bon, hydrogen, and o.xygen), arc essential to all living bodies, while a 
fourth element (nitrogen) may be almost considered peculiar to animals. 
We shall now proceed to describe the various kinds of meshes, of which 
the network is composed, and the different combinations into which these 
four elements arc found to enter. 
There arc three kinds of organized principles, or forms of network; 
the cellular tissue, the medullary substance, or marrow, and the muscular 
fibre. To eacli of these forms is attached a peculiar combination of che- 
mical elements, as well as a particular function. 
The cellular substance is composed of an indefinite number of small 
lamina;, without any apparent arrangement, crossing so as to form very 
small cells, communicating with each other. It may be compared to a 
species of sponge, similar in form to the entire body ; while all other ani- 
mal particles either occupy its cells, or traverse its substance. It pos- 
sesses the property of contracting indefinitely when the causes, which 
preserved it in a state of extension, are removed. Tliis power retains 
the body witliin the limits, and in the form, assigned to it by Nature. 
The cellular substance, or tissue, enters into the composition of every part, forming 
regular series of cells. We find it equally in the brain, the eye, and the nerves, only 
somewhat finer in its texture than in the bones and muscles. Its cells move with fa- 
eiUty, and accommodate themselves to the motions of the body, being moistened, at the 
points of contact with the ailjacent cells, by a liquid, which lubricates them like the 
synovia, or oily fluid of joints, so as to facilitate their motion. 
When the cellular substance is compressed into compact plates, it 
forms laminm of various extent, called mambrancs. These membranes, 
when united into cylindrical tubes, more or less ramified, receive the 
name of vessels. The filaments, called fibres, are entirely composed of 
cellular substance ; and the bones are nothing more than cellular substance, 
rendered bard by the deposition of earthy particles. 
The general matter of which the cellular substance is composed, con- 
sists in the proximate principle or combination, called gelatine; the dis- 
tinguishing character of which is, that it can be dissolved by boiling water, 
and, upon cooling, takes the form of a tremulous jelly. 
Gelatine, when analyzed by Gay-Lussac and Thenard, was found to contain in 100 
parts, by weight — carbon, 48; hydrogen, 8; oxygen, 27; and nitrogen, 17; very 
nearly. 
The medullary substance cannot bo resolved into any simpler organic 
structure. It appears to the eye as a soft wliitish pulpy matter, com- 
posed of an infinite number of very minute globules. No peculiar mo- 
tions can he observed in it ; but it possesses that most wonderful of all 
properties, the power of transmitting to the mind the impressions made 
on the external organs of sense, and of rendering the muscles subser- 
vient to the determinations of the will. The brain and spinal marrow arc 
almost entirely composed of medullary substance; and the nerves, which 
are distributed through all the organs capable of sensation, arc, in respect 
to their composition, nothing but bundles (or fasciculi) of this substance. 
The muscular, or fleshy fibre, is composed of a particular kind of fila- 
ments, having the peculiar property, during life, of contracting or folding 
themselves up, when touched or injured by any external body; or when 
acted upon, through the medium of the nerves, by the will. 
The muscles are the immediate organs of voluntary motion, and are 
composed entirely of bundles of fleshy fibres. All the membranes and 
vessels, which are required to exercise any compressive force, are armed 
with these fibres. They are alwa)-s united intimately with the nervous 
filaments, or threads ; but certain muscles are observed to execute mo- 
tions, altogether independent of the will, especially in the exercise of func- 
tions possessed in common with plants. Thus, although the wdll is fre- 
quently the cause of muscular motion, yet its power is neither general 
nor uniform in its action. 
Fleshy fibre lias, for the basis of its composition, a particular principle. 
■atm&di fibrin, which is [nearly] insoluble in boiling water, and seems na- 
turally to assume a filamentous arrangement. 
It consists of white solid fibres, inodorous and insipid. Wlien analysed by Gay- 
Lussac and Thenard, 100 parts were found to contain about 53 parts of carbon, 7 of 
hydrogen, 20 of oxygen, and 20 of nitrogen. 
The nutritive fluid, or blood, when recently extracted from the circulat- 
ing vessels, may not only be ultimately resolved, for the most part, into the 
general elements of the animal body, carbon, hydrogen, oxygen, and nitro- 
gen; but it already contains fibrin and gelatine, prepared to contract the:'' 
substance, and to as.sumc respectively the forms of filaments or of mca'" 
branes, according to circumstances, whenever a slight repose enables them 
to exhibit this tendency. In addition to these, the blood contains an- 
other proximate principle, called albumen, [composed very nearly of 
parts of carbon, 7 of hydrogen, 24 of oxygon, and 16 of nitrogen.] 
character is to coagulate in boiling water, [like the white of eggs, com- 
posed almost entirely of albumen.] We also find in the blood nearly a 
the other elements, which enter into the composition of each animal hot y 
in small quantities ; such iw, the lime and phosphorus deposited in t 
bones of the liiglier animals ; the iron, whicli seems essential to the colouf 
