36 
THE SOUTHERN CULTIVATOR, 
LIEHIG’ri ANIMAL CilEMISTIlY. 
The ancients held that all bodies were com- 
posed of fire, air, earth and water, which they 
called elements. The chemists of the present 
day enuirrerate fifty-five elements. Of these 
only a few enter into the composition of organic 
beings. Into the texture of plants and animals 
minute portions of lime, iron, silex, soda, pota.sh, 
sulphur and phosphorus enter; but it is carbon, 
nitrogen, oxygen and hydrogen, that constitute 
the main bulk of their solids and juices. These 
last are the alphabet, so to speak, out of which 
the beautiful volume of the living world has 
been compo.sed. Widely as plants and animals 
differ in outward show from the atmosphere 
they breathe and the soil in which they are fixed 
and on which they tread, they present on analy- 
sis no element which is not found in the mine- 
ral kingdom. It may well excite surprise that 
the blood, mantling in the cheek of female beau- 
tv, and tlie brain which gives manifestation to 
the mind of the orator and poet — that the muscle 
of the herculean frame, the viper’s venom, the 
food that nourishes, and the vegetable poisons 
that destroy, the nectar of flowers and the noi- 
some exlialation of marshes, all, however varied 
in form or opposed in quality, consist of these 
four elements in endless combinations— all de- 
rive their shape and strange diversity of attri- 
butes from varying proportions of oxygen, car- 
bon, nitrogen and hydrogen. 
Animals and vegetables agree, in deriving 
their existence from parents, in growing from 
.small beginnings to a determinate size, and then 
Yielding up the living principle, and mouldering 
into the elements from which they grew, by 
which they are ea.sily distinguished from the in- 
organic matter which constitutes the mineral 
world. Animals grow by imbibing oxygen and 
eliminating carbonic acid; vegetables, on the 
other hand, absorb carbonic acid, retain its car- 
bon, and emit the oxygen. They both live in 
the atmosphere, which is equally indispensable 
to either race, but each derives support from 
matters given out from the other. They would 
alike perish in an atmosphere of carbonic acid, 
but while this gas is exhaled continually from 
the lungs and breathing pores of every animal, 
it is greedily drunk up by the green vegetable, 
and aids in its nourishment and growth. 
Liebig has written with singular ability on 
the functions of both classes of vital beings. — 
His admirable treatise on vegetable physiolo^ 
and agriculture has been repeatedly noticed in 
our paper, and we propose now to give an out- 
line of his theory of animal chemistry, 
A few years ago, very little was known of the 
chemistry of organic beings. Anal 3 "sis, it is 
true, had been efiected of many animal and ve- 
getable products; and isolated facts, the value of 
which was not appreciated, were scattered over 
the pages of writers on physiology and chemis- 
try. A rude attempt was made at an early peri- 
od in the history of these sciences to explain 
upon chemical laws some of the functions of 
animal beings, but these speculations, for the 
most part, were eminently and even ridiculously 
abortive. Where the early chemists hit upon 
the right track they were soon lured from it by 
the absurd philosophy of their times, and their 
best efforts were but slight approximations to the 
truth. But their labors multiplied the materials 
of the science, and out of the shapeless mass of 
observations which has been .steadily increasing, 
the beautiful .system of Liebig has emerged. — ■ 
Since the time of Dr, Black, some of the great 
minds in every period have been busy at work 
upon the foundations of animal chemistrjq and 
the science has at last as.sumed a shape which 
promises to be enduring. The honor of rearing 
the edifice will generally be ascribed to Liebig, 
but this is not entirely just, for, on many points, 
the most that he can claim is the credit of having 
worked into a system facts which others had es- 
tablished. This, indeed, was a great work, re- 
quiring a genius of a high order; nor is it the 
only merit which belongs to this author. He 
has verified results, in numerous instances, by 
repeating experiments with the utmost care and 
precision; and he has added by his original re- 
searches many important facts to our stock of 
knowledge on several subjects connected with 
the functions of living beings. In his hands 
the materials have been classified and arranged, 
and have assumed the character of genuine .sys- 
tematic science. Y/e have no hesitation in sa}''- 
ing that he is one of the first philosophers of the 
age, and that the present, like his former work, 
will compare in logical clearness and original 
speculation with any that has been produced in 
modern times. 
The power in animals of maintaining an 
equable tempei’ature under great differences of 
exposure, is one Avhieh has engaged the atten- 
tion of physiologists since the earliest ages. A 
man, it has been proved by the most repeated 
observations, preserves the natural heat of his 
body Avhatever may be the temperature of the 
climate in which he lives. At Palermo, or Al- 
giers, where Fahrenheit’s thennometer, in the 
shade often rases to 100 degree.s, the temperature 
of his blood does not grow warmer than his hy- 
perborean brother, who is exposed to an atmos- 
phere that frequently sinks the thermometer 
many degrees below zero. What makes the 
case .still stronger, men have often been shut up 
fora .short time in a room, the air of which was 
heated far above the boiling point of water — to 
a temperature high enough to broil a beef-steak 
and boil vegetables, without suffering any decid- 
ed rise of their OAvn temperature. These are 
curious facts, illustrating forcibly the indepen- 
dent temperature of animals; and this reinarka- 
ble function is one of the problems to the solu- 
tion of which Liebig has devoted a considera- 
ble portion of his work. With Dr. Black, La- 
voisier, Crawford and others, he regards respi- 
ration as* a process of combustion, and as we 
warm our apartments by burning coal and wood, 
so we keep up the wannth of our bodies by 
burning portions of our food, Avhich v'e take in 
as fuel. The animal body, according to this 
doctrine, resembles a furnace — the food corres- 
ponding to the fuel, and the oxygen of the at- 
mosphere serving, as it does in the furnace, to 
consume the fuel and evolve heat in the process. 
Lavoisier has shown that a man of ordinary 
size, and in perfect health, consumes more than 
seven hundred pounds of oxygen in the course 
of the year, without gaining in weight. The 
man, during this time, has been taking food every 
day, and Liebig proves very clearly that a large 
portion 0 l it must have united with the oxygen 
to form the carbonic acid, fifty thousand cubic 
inches of which are daily exhaled from the lungs 
of an adult. Now the conversion of carbon into 
carbonic acid is essentially a heating operation. 
It never takes place without the extrication of 
heat. The union is rapid in our fire-places, and 
the quantity of caloric emitted in a given time 
is very great; but the amount of heat generated 
by the comoustion of a specific quantity of car- 
bon is a fixed quantity. It is evolved slowly 
from the mass of fermenting vegetable matter, 
from the malting grain, for example, and from 
the heap of half-cured hay, but the number of 
degrees of heat thus given out is not le.ss, for the 
quantity of carbonic acid formed, than if the 
combination had been the work of a few mo- 
ments. 
A man in good health, and taking moderate 
exercise, con.sumes, according to our author, 
nearly fourteen ounces of carbon daily, which 
escapes in due time, as carbonic acid, through 
the lungs and skin. For the conversion of so 
much carbon into the acid, thirty-seven ounces 
of oxygen are necessary, and in this union, 
which takes place in the body every four-and- 
twenty hours, 195,531 degrees of heat must be 
liberated— an amount sufficient to cause 68 lbs. 
of Avater at 32 degrees to boil; or to heat 184 lbs. 
to the temperature of the human body. If to 
this, the heat evolved by the hydrogen of the 
food, during its conversion into water by oxida- 
tion Avithin the body, be added, Ave shall find the 
quantity amply sufficient to explain the uniform 
temperature of the human body. 
But, in order to maintain this constant tem- 
perature, the supply of food and of oxygen must 
vary Avith the changes of atm0.spherical heat 
and cold to which the individual is subjected. 
He must take more food in cold climates than 
in hot, and more in winter than in summer, and 
his food must also be of a richer quality. And 
this is the ca'^ e Avith the inhabitants of high 
northern latitudes. The Russian, amid the 
snows of the qrcdc circle, devours the raw flesh 
of the deer, and drinks its wann blood as it 
flows from the body; and the Esquimaux will 
eat ten pounds of flesh and perhaps a dozen tal- 
loAV candles into the bargain, daily, without the 
slightest fear of indigestion. The people, on 
the contrary, who inhabit a climate but little be- 
low the temperature of their bodies, subsist 
chiefly upon fruits which contain a small pro- 
portion of carbon. At the north, such fruits 
could not be matured, nor would they be suited 
to the wants of the inhabitants. It is animal 
food, and that of the fattest qualitj’', that they 
need to supply their systems with the requisite 
amount of fuel. Children, for the reason that 
respiration in them is moi e active than in adults, 
require to be fed oftencr; and birds, having large 
lungs in proportion to their bodies, die of hun- 
ger in as many days as it takes months to starve 
serpents Avffiich breathe sloAvly "and consume lit- 
tle oxygen. The animal heat of the two tribes 
of creatures is correspondent. That of birds is 
higher than the temperature of man; that of the 
reptile is but two or three degrees above the tem- 
perature of the surrounding atmosphere. 
The food of animals, therefore, performs a 
tAVo-Ibld office — it contributes to the nourishment 
of their bodies, and it furnishes the fuel by 
which animal heat is developed. This is one 
of the most striking and original of Liebig’s 
doctrines, according to which the aliment of an- 
imals consists of tAco classes of substances, des- 
tined to perform altogether different purposes in 
their economy. The first he calls the niirogen- 
ized elements of lood, or the plastic elements oj 
nutrition, Avhich go to make blood, and execute 
the various offices ol growth and reproduction; 
and the second elements, which 
do not contribute to the nourishment of the body, 
but are consumed in the production of animal 
heat. Milk, which is the food of the young an- 
imal of so many .species, contains both elements. 
The ca.seine, or cheese, is the portion Avhich 
nourishes; it contains the materials for making 
blood, for the formation of bone, and the other 
functions of its immature system, whilst the 
sugar of milk, and the butter supply it Ayith fuel. 
In Avheat, and other grains of this class, as also 
in the potato, though not to an equal extent, the 
same admirable combination exists, and these 
are the chief articles of food for man and for his 
dome.stic animals, in nearly all the temperate 
regions of the globe. The nutritious principle 
is contained in the gluten; the fqel in the starch, 
the oil and the sugar. In proportion to the cold 
to which the animal is exposed, is the consump- 
tion of oxygen and of fuel; apd as the same is 
true of exercise, it folio avs that men and animals 
who are compelled to labor must be better fed, 
and that even with an ample allowance of food, 
if their labor is severe, they do not groAV fat. — 
The starch, sugar and other elements which 
would be converted into fat, are entirely consum- 
ed by the process of respiration. If, with the 
same allowance of food, these individuals are 
permitted to take less exercise, the fuel is but 
partially consumed; and a deposite of fatty mat- 
ter is the consequence. Thisis shown constant- 
ly in the hog and in the whale, animals which 
eat largely in proportion to the oxygen consum- 
ed— in other Avords, to the exercise they take— 
and which consequently grow exceedingly fat. 
It is seen in the bear also, and in the opossum, 
in which the fat would seem to perform the dou- 
ble office of protecting them against the external 
cold, and of supplying the internal heat necessa- 
ry to maintain life during the frosts of winter. 
And the opposite phenomena are observed in the 
deer, and animals that like it are active in their 
habits, the flesh of which is always compara- 
