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Alexander von Humboldt: „On the Cow Tree of the Caraccas, and on the Milk of Vegetables in general“, in: ders., Sämtliche Schriften digital, herausgegeben von Oliver Lubrich und Thomas Nehrlich, Universität Bern 2021. URL: <https://humboldt.unibe.ch/text/1818-Sur_le_Lait-21-neu> [abgerufen am 25.05.2024].

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Titel On the Cow Tree of the Caraccas, and on the Milk of Vegetables in general
Jahr 1819
Ort London
Nachweis
in: The Repertory of Arts, Manufactures, and Agriculture 35:205 (Juni 1819), S. 55–60.
Sprache Englisch
Typografischer Befund Antiqua; Auszeichnung: Kursivierung; Schmuck: Initialen.
Identifikation
Textnummer Druckausgabe: III.56
Dateiname: 1818-Sur_le_Lait-21-neu
Statistiken
Seitenanzahl: 6
Zeichenanzahl: 10003

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|55|

On the Cow Tree of the Caraccas, and on the Milk ofVegetables in general. Extracted from a Memoir on thisSubject, by A. de Humboldt. From the Annales de Chimie et de Physique.

We had for several weeks (says M. Humboldt) heardspeak of a tree growing in the vallies of Aragua, whosejuice was a nutritive milk, and hence called the cow tree, palo de vaca; and we were assured that the negroes of thefarm, who drank abundantly of this milk, consider it asa very wholesome food. As all the milky juices of plantshitherto known were either acrid or bitter, and more orless poisonous, this assertion appeared to us extraordi-nary; but experience has shewn us, during our stay atBarbula, (a province of the Caraccas,) that the virtues ofthe palo de vaca had not been exaggerated. This beau-tiful tree has the appearance of the chrysophyllum caimita: its leaves are oblong, pointed at the extremities, coria-ceous and alternate, and are marked with lateral ribs,raised from below the leaf, and parallel; their length isabout ten inches. We did not see the blossom: the fruitis somewhat fleshy, and contains one and sometimes twonuts. When incisions are made in the trunk of the tree, itgives an abundance of thick glutinous milk, not at allacrid, and which exhales an agreeable smell of balsam.We drank it out of calebash shells, in considerablequantity, both night and morning, without finding anyunpleasant effects from it. The clamminess alone madeit a little disagreeable. The negroes and free servants ofthe plantations dip their manioc and cassava bread in it: |56|and the overseer assured us, that the slaves become sen-sibly fatter in the season in which the palo de vaca yieldsthe most milk. When exposed to the air this milk be-comes covered, perhaps owing to the absorption of oxy-gen, with membranes of a strongly animalised, yellowish,cheesy matter, which may be drawn out into threads.These membranes, when taken out of the liquid, are elas-tic, almost like caoutchouc; but after a time they pu-trefy like gelatine. The common people give the nameof cheese to the coagulum which separates from this milkby the contact of air: this cheese grows sour in five orsix days. When the milk was enclosed in a corked bottle itdeposited a little coagulum, but far from becoming offen-sive, it exhaled a balsamic smell. The fresh juice mixedwith cold water would hardly coagulate, but the viscousmembranes separated on the addition of nitric acid. The extraordinary tree of which we are speaking, ap-pears to be peculiar to the cordillera du littoral, particu-larly from Barbula to the lake of Macaraibo. Somestems of it are also to be found near the village of SanMateo, and, according to Mr. Bredmeyer, whose travelshave so much enriched the gardens of Schonbrunn andVienna, it is met with the valley of Caucagna, three daysjourney east of Caracca. This naturalist has found, aswe have, this vegetable juice to be of an agreeable taste,and an aromatic smell. The natives call the tree Arbolde Leche, Milk Tree. Long before chemists had detected small portions ofwax in the pollen of flowers, the varnish of leaves, andthe white efflorescence on our plums and grapes, the in-habitants of the Andes of Quindiu made candles of thethick coating of wax which covers the stems of the palmtrees. It is but a few years since the caseum, the basis |57|of cheese, has been discovered in almond emulsion; andyet, for centuries, in the mountains near Venzuela, themilk of a tree, and the cheese separating from this milk,have been regarded as a salutary food. What can be thereason of this singular order in the developement ofknowledge? How have the common people of one hemi-sphere made discoveries which have so long eluded thesagacity of skilful and enlightened chemists in the other?It is, because but a small number of elements and prin-ciples, differently combined, are unequally distributed indifferent families of plants; and because people that de-rive almost all their food from the vegetable kingdom, de-tect farinaceous and nutritious matter wherever naturehas deposited it, whether in the sap, the bark, the root,or the fruit of vegetables. The amylaceous feculum,which the grains of the cerealia offer in so much purity,is found in the root of the Arum, and the Jatropha Ma-nioc, united to an acrid and sometimes venomous juice.Hence the untutored native of America, and of the SouthSea Isles, has learnt to dulcify the feculum, by pressingout and separating the juice. In the milk and milkyemulsions of plants, substances eminently nutritious, suchas albumen, caseum, and sugar, are mixed with caout-chouc and acrid deleterious principles, such as morphineand hydro-cyanic acid. I shall add the results of some experiments which Imade on the juice of the papaw (Carica papaya) duringmy residence in the vallies of Aragua, though I was thenalmost entirely deprived of chemical re-agents. The samejuice has been since examined by Vauquelin; and thiseminent chemist has fully detected the presence of albumenand casiform matter: he has compared the milky juice ofthe papaw to a strongly animalised substance, like theblood of animals; but he could only examine a juice that |58|had fermented and formed a fetid coagulum during thevoyage from the Isle of France to Havre; and he ex-pressed the wish that the papaw juice could be examinedas soon as it had flowed from the fruit stem. The younger the fruit is, the more abundant is itsjuice: it is even found in the germ before fecundation.As the fruit ripens, the milk diminishes in quantity, andbecomes more watery; and contains less of this animalmatter, which is coagulable by acids, and by exposure toair. As the whole fruit is viscous, it may be presumedthat in proportion as it becomes larger, the coagulablematter is deposited in its organs, and contributes to formthe pulp, or the fleshy portion. When nitric acid, dilutedwith four parts of water, is poured drop by drop into theexpressed juice of a very young fruit, a singular appear-ance is observed: there forms in the centre of each dropa gelatinous pellicle, divided by grey striæ. These striæare only the juice, rendered more watery by the contactof the acid which has separated its albumen. At thesame time the centre of each pellicle becomes opake andyellow, like the yolk of an egg, and these pellicles gradu-ally enlarge, as if by the prolongation of diverging fibres.All the liquid at first has the aspect of clouded agate, andthe organic membranes appear to shoot up under theeye. When the coagulum extends over the whole mass,the yellow spots again disappear, and on stirring the li-quid it becomes granulated like soft cheese. The yellowre-appears on adding fresh nitric acid. The acid here hasthe same action as the contact of atmospherical oxygenat a moderate temperature, for the white coagulum be-comes yellow in two or three minutes when exposed tothe sun. In some hours more the yellow colour passesinto shades of brown, doubtless because the carbon be-comes more free in proportion as the hydrogen with |59|which it was united undergoes combustion. The coagu-lum by nitric acid becomes viscous, and takes that pe-culiar waxy smell which I have observed before in treat-ing the fleshy part of truffles with nitric acid. Mr.Hatchett’s interesting experiments would lead me to sup-pose that the albumen is partly converted to gelatine.The fresh coagulum of the papaw softens in water, ispartly dissolved, and tinges the liquid yellow. The milkyjuice, put in contact with water, forms also these mem-branes, and there immediately falls down a sparklingjelly, like starch. This appearance is still more strikingif the water is heated from 100° to 140° Fahrenheit. Thejelly is more condensed as the water added is greater.It long preserves its whiteness, and only becomes yellowby nitric acid. In imitation of Fourcroy and Vauquelin’s experimenton the juice of the hevea, I added to a solution of papawmilk some carbonate of soda. No coagulum was formed,and the membranes only appeared when the excess ofsoda was neutralised, or more than neutralised by an acid.In the same manner I dispersed the coagulum formed bynitric acid, by lemon-juice, or by hot water; and mixingit with carbonate of soda, the juice becomes againmilky as in its original state, but this experimentsucceeds only when the coagulum has been recentlyformed. In comparing the milky juices of the papaw, the palode vaca, and the hevea, one may see a striking analogybetween the juices that contain casiform matter, andthose in which caoutchouc predominates. All the whitefresh preparations of caoutchouc, as well as the water-proof cloaks made in Spanish America, by covering thecloth on each side with the caoutchouc juice, exhale a |60|nauseous animal odour. This seems to shew that caout-chouc in coagulating carries with it the caseum, which isperhaps only albumen a little altered. The bread-fruit isno more identical with bread than are the bananas beforematurity, or the tuberous and amylaceous roots of the manioc, the dioscoreæ, the convolvulus batatas, and thepotatoe. On the other hand, the milk of the cow-treecontains real casiform matter, like the milk of the mam-miferæ. Speaking in general terms therefore, we may,with Gay-Lussac, consider the caoutchouc as the oilyprinciple, or the butter of vegetable milk, the latter con-taining caseum and caoutchouc, as animal milk holds ca-seum and butter. These two principles differ in their re-spective proportions, both in the animal and vegetablemilks. With the latter are often also mixed other prin-ciples, noxious as food, but which may perhaps come tobe separated by chemical means. Every vegetable milkbecomes more fitted to be the food of man, in proportionas it is deprived of acrid and narcotic principles, and asthe casiform matter predominates over the caoutchouc.