are sometimes called the histogenetic bodies or proteids,
because they are essential to the building up of the animal
organism. The vegetable kingdom is the original source of
albuminous substances, the albumins being found in greatest
quantity in the seed. They also occur in the fluids of the
living organism. The chemistry of the albumins is one of
the most complicated and difficult in the whole domain of
organic chemistry. It has attracted the attention of many
workers, and has formed the subject of a huge literature.
In this field Bechamp, Cohnheim, Albrecht Kossel, and,
especially, Emil Fischer and his pupils have been extremely
active. The general trend of these researches lies in the
study of the decomposition or ``breaking down'' products of
the albumin molecules; once these are accurately determined,
the synthesis of an albumin is but a matter of time. Already
we have proceeded far in our knowledge of the decomposition
products, and certain simple proteids have been synthesized.
General characters.
The albumins contain in all cases the elements carbon, hydrogen,
nitrogen, sulphur and oxygen; their composition, however,
varies within certain limits: C = 50-55%, H = 6.9-7.3%, N. =
15-19%, S = 0.3-2.4%, O = 19-24%, crystallized albumin is C =
51.48%, H = 6.76%, N = 8.14%, S = 0.96%, O = 22.66%, which
points to the formula C720H1134N218S5O248,
corresponding to the molecular weight 16,954. A high molecular
weight characterizes these substances, but so far no definite
value has been determined by either physical or chemical means;
A. P. Sabanezhev obtained the value 15,000 by Raoult's method
for purified egg albumin. All albumins are laevo-rotatory; and
on incineration a small amount of inorganic ash is invariably
left. They are usually insoluble in water, alcohol and ether;
and their presence as solutes in vegetable and animal fluids
is not yet perfectly understood, but it is probably to be
connected with the presence of salts or other substances. A
remarkable change occurs when many albumins are boiled with
water, or treated with certain acids, their solubility and
general characters being entirely altered, and the fluid becoming
coagulated. This change is seen in the transformation of the
``white'' of an egg on boiling. Albumins are generally detected
by taking advantage of this property, or of certain colour
changes. The reagents in common use are: Millon's reagent,
a solution of mercuric nitrate containing nitrous acid, this
gives a violet-red coloration; nitric acid, which gives a
yellow colour, turning to gold when treated with ammonia
(xanthoproteic reaction); fuming sulphuric acid, which gives
violet solutions; and caustic potash and copper sulphate, which,
on warming, gives a red to violet coloration (biuret reaction).
Decomposition products.
Boiling with dilute mineral acids, or baryta water, decomposes
albumins into carbon dioxide, ammonia and fatty amino- and other
acids. These decomposition products include: glycocoll or
aminoacetic acid, NH2CH2COOH, alanine or aminopropionic
acid, CH3.CH(NH2).COOH, a-aminobutyric acid,
a-aminovalerianic acid, leucin or isobutyl-a-aminoacetic
acid, (CH3)2CH.CH2.CH(NH2).COOH, isoleucin, probably
b-aminocaproic acid, serin or a-amino- b-hydroxypropionic
acid, HO.CH2.CH(NH2).COOH, aspartic acid or aminosuccinic
acid, HOOC.CH2.CH(NH2).COOH, glutaminic acid or a-amino-
n-glutaric acid, HOOC.(CH2)2.CH(NH2).COOH, diaminoacetic acid,
a-b-diaminopropionic acid, lysin. or a-e-diamino-n-caproic
acid, NH2(CH2)4.CH(NH2).COOH, arginin or guanidine-a-amino-
n-valerianic acid, (NH)(NH2)C.NH.(CH2)3.CH(NH2).COOH,
ornithin or ad-diamino valerianic acid,
NH2.(CH2)3.CH(NH2).COOH, histidin or a-amino- b-imidazol-
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propionic acid HOOC.CH(NH2).CH2.C:CH.N:CH.NH, proline
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or a-pyrrolidin carboxylic acid, HOOC.CH.NH.CH2.CH2.CH2,
hydroxyproline, phenyl alanine or phenyl-a-aminopropionic
acid, C6H5.CH2.CH(NH2).COOH, tyrosine or p-hydroxyphenyl-
a- aminopropionic acid, phenyl ethylamine, p-hydroxyphenyl
ethylamine, tryptophane or indol aminopropionic acid,
A. cystin (protein-cystin) or a-amino-b-thioglyceric
acid ``disulphide,'' (S.CH2.CH(NH2).COOH)2, B.
cystin (stone-cystin), or a-thio-b-aminoglyceric acid
``disulphide,'' (NH2.CH2.CH:S.COOH)2. This list is
not exhaustive; other products are given in Gustav Mann,
Chemistry of the Proteids (1906), to which reference should
be made for a complete account of this class of compounds.
Classification of albumins.
The complexity of composition militates in a great measure
against a rational classification of albumins by purely chemical
considerations. Such classifications have been attempted by
A. Kossel and by W. Kuhne and E. P. Pick; but in the present
state of our knowledge, however, the older classification
of E. Dreschel and F. Hoppe- Seyler, based primarily on
solubilities and distribution, may be conveniently retained.
This classification is with certain modifications as follows:-
I. Albumins proper: characterized by having colloidal solutions.
(1) Albumins: serum-albumin, egg-albumin, albumin.
(2) Globulins: serum-globulin, egg-globulin, lacto-
globulin, cell-globulins.
(3) Plant-globulins and plant-vitellines.
(4) Fibrinogen.
(5) Myosin.
(6) Phosphorus containing albumins (nucleo-albumins),
caseins, vitellines, nucleo-albumins of the cell-
protoplasm, mucoid nucleo-albumins.
(7) Histones.
(8) Protamines.
II. Transformation products of the albumins proper.
(1) Acid-albumins, alkali albuminates.
(2) Albumoses, peptones and peptides.
(3) Halogen-albumins, oxyprotein, oxyprotsulphonic
acid, &c.
III. Proteids.
(1) Nucleo-proteids.
(2) Haemoglobin and allied substances.
(3) Glyco-proteids, mucins, mucoids, helico-proteid.
IV. Albuminoids.
(1) Collagen.
(2) Keratin.
(3) Elastin.
(4) Fibroin.
(5) Spongin, &c.
(6) Amyloid.
(7) Albumoid.
(8) Colouring matters derived from albumin.
Albumins proper.--Albumins (as classified above) are
soluble in water, dilute acids and alkalies, and in
saturated neutral salt solutions; they are coagulated by
heat. ``Serum- albumin,'' or ``blood-albumin,'' possibly
C450H720N116S6O140, occurs in blood-serum,
lymph, chyle, milk, &c.; its coagulation temperature is about
67 deg. . It differs from egg-albumin in its specific rotation
(-57 deg. to -64 deg. ), and in being slowly coagulated by alcohol and
ether. Egg-albumin is the chief constituent of the white
of egg; this fluid also contains a globulin and a mucoid.
It coagulates at about 56 deg. , and its specific rotation is
-30.70 deg. . ``Lact-albumin'' occurs in all kinds of milk.
The globulins are insoluble in water and in dilute acids,
but soluble in alkalies and in neutral salt solutions; these
solutions are coagulated on boiling. ``Serum-globulin,'' also
termed globulin or fibrino-plastic globulin, paraglobulin and
paraglobin, occurs in blood serum; ``cell-globulins'' occur
in many organs--liver, kidneys, pancreas and the thyroid
gland, also in muscle-plasma; ``crystalline,'' a globulin
occurring in two forms a and b, is found in the lens
of the eye; ``egg-globulin'' and ``lacto- globulin'' occur
respectively in the white of egg and in milk. Plant albumins
or phyto-albumins have been chiefly investigated in the case
of those occurring in seeds; most are globulins, insoluble
in pure water, but soluble in salt solutions; ``edestin,''
a globulin of this class, is very widely distributed. Other
varieties or classes of these compounds are: plant caseins,
phyto-vitellines, legumins and conglutins. Fibrinogen
occurs in the blood plasma, and is changed by a ferment into
fibrin, to which the clotting of blood is due. Fibrinogen
is insoluble in water, but soluble in salt solutions; it
has three different coagulation temperatures, 56 deg. , 67 deg. ,
75 deg. . Fibrin, produced from fibrinogen by a ferment, is
a jelly-like substance, coagulable by heat, alcohol, &c.
The muscle-albumins include ``myosin'' or paramyosinogen, a
globulin, which by coagulation induces rigor mortis, and
the closely related ``myosinogen'' or myogen; myoglobulin and
myoalbumin are also found in muscles. The nucleo-albumins
or phospho-globulins are insoluble in water and acids, but
soluble in alkalies, and have an acid reaction. ``Caseinogen''
(after W. D. Halliburton) is the chief albumin of milk;
its composition varies with the animal. It is insoluble in
water, while its salts are readily soluble. ``Eucasein'' is
the ammonium salt; ``nutrose'' and ``plasmon'' are sodium
salts. By the rennet ferment caseinogen is converted into
casein, a substance resembling caseinogen in being soluble
in water, but differing in having an insoluble calcium
salt. The formation of casein involves the curdling of
milk. Other phosphoglobulins are vitelline, found in the
yolk of hens' eggs, and ichthulin, found in the eggs of
fish. Histones are a class of albumins soluble in water
and acids, but essentially basic in character; hence they
are precipitated by alkalies. It is remarkable that many
histones are soluble in an excess of alkali. They do not
exist in a free state, but in combination with a ``prosthetic
group'' (after A. Kossel) they give rise to important cell
constituents--haemoglobin, nucleo-proteids, &c. ``Thymus histone''
occurs in the thymus gland; globin occurs in combination as
haemoglobin; other histones have been extracted from the red
blood corpuscles of the goose and the testes of fishes and
other animals. The protamines are a well-characterized
class of albumins found in the ripe spermatozoa of fishes.
Albumoses and Peptones.--The primary products of the dissociation
of albumins are the albumoses, characterized by not being
coagulable by heat, more soluble than the albumins, having a
far less complex composition, and capable of being ``salted
out'' by certain salts, and the peptones, similar to albumoses
but not capable of being ``salted out''; moreover, peptones
are less complex than albumoses. By further decomposition
peptones yield peptides, a certain number of which have been
synthesized by Emil Fischer and his collaborators. Albumoses
and peptones are white powders, readily soluble in water, with
the exception of the hetero-albumoses--a subdivision of primary
albumoses. They give the biuret and xanthoproteic reactions,
and form salts with both acids and bases. Albumoses and
peptones are obtained by peptic digestion, the latter being
termed peptic- peptones; tryptic digestion also produces
peptones. Acids and moist heat induce similar changes.
Proteids.--These substances are combinations of one or more
albumins with a radical of an essentially different nature,
termed by Kossel a ``prosthetic group.'' It is convenient
to classify proteids by those groups. ``Nucleo-proteids,''
constituents of the cell-nucleus, are combinations of albumins
and nucleic acid; they always contain iron. They are loose,
white, non-hygroscopic powders, soluble in water and salt
solutions, and have an acid reaction; they give the colour
reactions of albumins. Nucleic acid is at present of unknown
constitution; decomposition products are: phosphoric acid, uracil
or 2.6-dioxy-pyrimidin,1 cytosin or 2-oxy-6-amino-pyrimidin,
