Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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The Membranes Appear Only When, By Adding An Acid,
The Soda Is Neutralized, And The Acid Is In Excess.
I made the
coagulum formed by nitric acid, the juice of lemons, or hot water,
likewise disappear by mixing it with carbonate of soda.
The sap again
becomes milky and liquid, as in its primitive state; but this
experiment succeeds only when the coagulum has been recently formed.
On comparing the milky juices of the papaw, the cow-tree, and the
hevea, there appears a striking analogy between the juices which
abound in caseous matter, and those in which caoutchouc prevails. All
the white and newly prepared caoutchouc, as well as the waterproof
cloaks, manufactured in Spanish America by placing a layer of milk of
hevea between two pieces of cloth, exhale an animal and nauseating
smell. This seems to indicate that the caoutchouc, in coagulating,
carries with it the caseum, which is perhaps only an altered albumen.
The produce of the bread-fruit tree can no more be considered as bread
than plantains before the state of maturity, or the tuberous and
amylaceous roots of the cassava, the dioscorea, the Convolvulus
batatas, and the potato. The milk of the cow-tree contains, on the
contrary, a caseous matter, like the milk of mammiferous animals.
Advancing to more general considerations, we may regard, with M.
Gay-Lussac, the caoutchouc as the oily part - the butter of vegetable
milk. We find in the milk of plants caseum and caoutchouc; in the milk
of animals, caseum and butter.
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