Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/179/
PROTEIN. 
very similar to that already mentioned when 
speaking of albumen: in the milk, which is 
the sole food on which the young of most ani¬ 
mals subsist, no other protein compound has 
been detected ; but no sooner has it become 
the food of the young animal which it is in¬ 
tended to nourish, than it is for the most part 
converted into fibrin and albumen, thus fur¬ 
nishing blood and muscle, together with most 
of the other tissues of the body, which, though 
less directly, are scarcely less certainly products 
of the decomposition of this substance. The 
composition of casein is represented by the for- 
mula C400 H310 Nso 0120 S, or ten equi¬ 
valents of protein united to one equivalent of 
sulphur, thus differing from fibrin and albu¬ 
men in not containing any phosphorus. 
There is another modification of protein, 
very similar to casein in its properties and 
composition, which has been called both glo¬ 
bulin and crystalline, from the circumstance 
that it is found surrounding the blood globules 
and also in the crystalline lens of the eye. It 
appears to contain no phosphorus and less sul¬ 
phur than casein, and is composed, according 
to Mulder, of fifteen equivalents of protein 
united to one of sulphur. 
The form in which protein exists in hair, 
horn, nails, and the epidermis, and called by 
Simon keratine, has been but imperfectly ex¬ 
amined. That these substances are composed 
chiefly of protein is proved by the circumstance 
that if a solution of them be made in caustic 
potash and neutralized with acetic acid, a co¬ 
pious precipitate of protein is thrown down. 
It is probable that other modifications of protein 
will hereafter be found to exist in the animal 
body, but those which I have now described 
are all which have hitherto been detected. 
The animal body, however, is not the only 
source from which protein and its compounds 
are to be obtained. The researches of modern 
chemists have led to the interesting fact that 
they exist in the vegetable kingdom also, and 
that they are there so extensively disseminated 
that not a leaf, a seed, or a twflg, in any of the 
various tribes of plants, is free from them ; and 
it is highly probable that the whole of the 
protein compounds constituting the bodies of 
animals are derived from plants. In the pre¬ 
sent state of analysis it is perhaps too much to 
say that the forms in which we find protein in 
vegetables are absolutely the same, with regard 
to the minute quantities of sulphur and phos¬ 
phorus, as those found in animals ; but as far 
as we are able to judge from similarity of pro¬ 
perties, we may safely divide them in the same 
way as the analogous animal principles ; viz. 
into vegetable fibrin, vegetable albumen, and 
vegetable casein. They all yield, when heated 
with strong hydrochloric acid, blue or purple 
solutions; and when they are digested with a 
solution of potash, and neutralized with acetic 
acid, protein is invariably produced. 
Vegetable fibrin is found most abundantly 
in the seeds of the cerealia, as wheat, oats, &c. : 
it is also found dissolved in the juice of most 
plants, especially that of grapes, carrots, tur¬ 
nips, and beetroot, from which it shortly sepa- 
169 
rates in the form of a flocculent precipitate 
when taken from the plant and allowed to 
stand. The readiest way of preparing it is to 
knead wheaten flour into a paste with water, 
and then wash it on a linen cloth with a stream 
of cold water until the whole of the starch is 
removed, which is known by the water passing 
through quite clear : the viscous mass which 
remains on the cloth is subsequently purified 
by washing with alcohol and ether, in both of 
which the fibrin is insoluble. When dry it is 
a hard horny-looking substance, semitranspa¬ 
rent, without taste or smell, and sufficiently 
heavy to sink in water, in which it is insoluble. 
Phosphoric and acetic acids readily dissolve it ; 
and it is reprecipitated in the form of white 
flocks from its acid solution by carbonate of 
ammonia and ferrocyanide of potassium, and 
yellowish by tincture of galls ; it is also preci¬ 
pitated by bichloride of mercury and some 
other metallic salts. It is perfectly soluble in 
solution of potash even when very dilute, and 
if the quantity of fibrin dissolved be large, the 
liquid loses its alkaline flavour. 
Vegetable albumen is found to exist very 
abundantly in the juices of most plants, and 
still more so in nuts, almonds, and other oily 
seeds, where it is usually associated with ca¬ 
sein. It may be easily recognized by boiling 
the expressed juice of any of the common cu¬ 
linary vegetables after the fibrin has separated, 
when it coagulates in a manner similar to ani¬ 
mal albumen. It may be obtained in a tole¬ 
rably pure state by boiling the filtered juice of 
any of the leguminosce, and washing the preci¬ 
pitate with alcohol and ether. It closely re¬ 
sembles animal albumen in properties, and is 
distinguished from vegetable fibrin by its so¬ 
lubility in water, and from vegetable casein by 
coagulating when heated. 
Vegetable casein has also been called legu- 
mine, from the circumstance of its being found 
most abundantly in the leguminosce, though it 
is by no means confined to that tribe of plants: 
it is also present in considerable quantity in 
company with albumen in most of the oily 
seeds, and in the juices of most nutritious 
vegetables. It may be obtained by the follow¬ 
ing process. Peas or beans should be soaked 
in moderately warm water for some hours until 
they are sufficiently soft to allow of their being 
mashed in a mortar : the pasty mass is then 
mixed with a large quantity of water, which 
dissolves the casein, and thrown upon a cloth 
to filter. The starch passes through the filter 
together with the solution of casein, and if 
allowed to stand, gradually subsides to the 
bottom : when the liquid is clear, it is decanted 
by means of a syphon, and slightly supersa¬ 
turated with acetic acid, which determines the 
precipitation of the casein in an impure state, 
but readily purified by washing with alcohol 
and ether. Vegetable casein resembles that 
obtained from milk in most of its properties ; 
gives the same insoluble skin when heated in 
contact with the air ; and is precipitated from 
its aqueous solution of alcohol and several of 
the metallic oxides : it is also thrown down by 
both vegetable and mineral acids, redissolving
        

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