October 8, 1870.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
281 
THE PROCESS OF NUTRITION. 
BY BARON LIEBIG. 
Sensation and exertion are tilings fundamentally 
different, though it may be a long while before the 
physiological intellect succeeds in drawing a sharp 
distinction between them. 
The plant is a magazine of sun-force which has 
been accumulated in its parts during their develop¬ 
ment, and this force stored up in the food material 
of animals is again manifested in the animal body; 
it is the manifold action of this force which comprises 
and determines all phenomena of animal life. Hence 
the elucidation of the laws obtaining in regard to 
that force should, above all tilings, engage the atten¬ 
tion of investigators. 
In a complex machine it constantly happens that 
interruptions of the work to be done are caused by 
the mere action of the mechanism itself: the driving 
bands stretch, or a screw gets loose, or there is a loss 
of power in consequence of friction between certain 
parts of the machine, and for this reason we find in 
large factories some one continually occupied either 
in finding out the causes of such impediments, or in 
providing a remedy for them according to the means 
at his disposal. 
This case presents a very slender and scarcely ac¬ 
curate representation of the problems with which the 
physician and surgeon are jointly concerned in deal¬ 
ing with the infinitely more complicated human ma¬ 
chine ; but their ultimate object is in all cases that 
of maintaining this machine in regular work and in 
good condition, so that out of the power generated in 
the machine, there may be a maximum amount re¬ 
maining available for the performance of intellectual 
and corporeal work. 
I have already mentioned the very remarkable fact 
that in feeding a dog with a mixture of fat and meat 
(the latter being in larger amount than requisite for 
the animal’s support), the excess of meat which is 
not accumulated in the body undergoes metamor¬ 
phosis, its decomposition not being hindered by the 
fat given with it in the food. 
This fact proves the existence of a cause which 
definitely limits the accumulation of those blood- 
constituents which are not applicable for increase of 
flesh, and it may be a question for the investigations 
of physiologists to decide whether this cause operates 
directly upon the colloidal albuminates of the blood, 
or whether its operation is restricted to those flesh- 
constituents which have passed info the circulation 
before assuming the colloidal condition. The opinion 
that the cause here referred to operates directly upon 
the albuminates of the blood, as such, can scarcely 
be reconciled with the phenomena observed during a 
state of hunger. 
According to what we know respecting the pro¬ 
cesses going on in the muscles, urea is not a direct 
product from muscle-constituents within the muscle 
itself, and the question as to the origin of urea, or 
as to the part of the body in which it is formed, is 
still one of great interest. 
Stokvis and Heynsius found urea in the liver of 
the mammalia, and they have expressed the opinion 
that it is formed in the liver from uric acid. Meiss¬ 
ner has also established by a very comprehensive 
investigation the fact that urea does occur in the 
liver. 
For appreciating the processes going on in the liver, 
which is in animals of the higher classes the most 
Third Series, No. 15. 
powerful apparatus in the whole body for splitting 
up material, it is essential to take into account the 
remarkable observation by Schmulewitsche* as to 
the formation of bile. Uric acid and the acids of the 
bile are nitrogenous compounds, and they must be 
regarded as derivatives of albumen; the same with 
regard to hippuric acid, creatin, glycocol, etc. More¬ 
over, sugar is formed in the liver. 
From the chemical point of view, which is alone 
to be considered here, a comparison of the composi¬ 
tion of blood-albumen, the acids of bile and other 
nitrogenous products, leads to a recognition of some 
very interesting relations of these substances amongst 
each other, and to blood-albumen: as purely cal¬ 
culated relations they possess no real value, but they 
may nevertheless be of some utility in suggesting 
problems for investigation. 
If to the formula which I have adopted for albu¬ 
men of blood,f there be added 20 equivalents of oxy¬ 
gen, we obtain exactly the elements of 12 atoms of 
uric acid, 2 atoms of cholic acid, 1 atom choleic 
acid, and 14 atoms of water. 
Blood-albumen 
20 Oxygen 
2 uric acid . . 
2 cholic acid . 
J 1 choleic acid . 
| 14 water . . 
^ 216 FT 16 9 ^27 ^2 ^63 
^20 
^ 216 ^ 169-^27 
So O s3 
c 60 h 24 n 24 
^36 
^104 B-S6 ^2 
0 24 
c 52 h 45 n 
So0 14 
h 14 
0 14 
^216 ^169 ^ 27 ^2 ^SS 
In like manner cholic acid contains the elements 
of hippuric acid, margaric acid, and a hydrate of car¬ 
bon ; by adding 2 equivalents of oxygen to 2 of cho¬ 
leic acid, we obtain the elements of cystin, choles- 
terin, margarin and carbolic acid. 
By the association of 4 equivalents of water with 
cholic acid, there may be produced leucin, oleic acid 
and carbonic acid. 
In 2 atoms of uric acid and 12 equivalents of 
water, there are the elements of 2 glycocol, 3 urea 
and 6 carbonic acid. 
From 4 equivalents uric acid and 22 equivalents 
water, there might be produced 2 creatin, 5 urea and 
14 carbonic acid. 
There would be no object in multiplying these calcu¬ 
lations, but I do not regard them as absolutely value¬ 
less, because a knowledge oi possible relations of this 
kind awakens attention to those which are actual , 
and in that way it may contribute towards paving the 
way to a comprehension of normal and pathological 
processes. In connection with the foregoing formulae 
the occurrence of cystin in the urine involuntarily 
calls to mind the formation of cliolesterin and the 
reverse, while the occurrence of leucin suggests the 
formation of oleic acid. 
In recent times several physiologists have occupied 
themselves with the question as to the origin of fat 
in the animal body. 
Fat being lion-nitrogenous, I believe that its 
formation must be in some way connected with the 
non-nitrogenous constituents of the food, though I 
do not dispute the possibility of its being produced 
from albuminates. 
According to the investigations of Voit, it appears 
* See ante, p. 113. 
f See Chemical Letters. 
