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Alexander von Humboldt: „On the Milk of the Cow Tree, and on vegetable Milk 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-14> [abgerufen am 24.03.2023].

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Titel On the Milk of the Cow Tree, and on vegetable Milk in General
Jahr 1818
Ort London
Nachweis
in: Annals of Philosophy; or, Magazine of Chemistry, Mineralogy, Mechanics, Natural History, Agriculture, and the Arts 12 (Juli–Dezember 1818), S. 115–117.
Sprache Englisch
Typografischer Befund Antiqua; Spaltensatz; Schmuck: Kapitälchen.
Identifikation
Textnummer Druckausgabe: III.56
Dateiname: 1818-Sur_le_Lait-14
Statistiken
Seitenanzahl: 3
Zeichenanzahl: 6237

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|115|

On the Milk of the Cow Tree, and on vegetable Milk in General. By M. Humboldt.*

M. Humboldt and his companions, in the course of theirtravels, heard an account of a tree which grows in the valleys ofAragua, the juice of which is a nourishing milk, and which, fromthat circumstance, has received the name of the cow tree. Asthe milky juices of plants are in general acrid, bitter, and evenpoisonous, M. Humboldt was at first scarcely disposed to creditthe account, but experience proved it to be correct. The tree in its general aspect resembles the chrysophyllumcainito; its leaves are oblong, pointed, leathery, and alternate,marked with lateral veins, projecting downwards, they areparallel, and are ten inches long. M. Humboldt had no oppor-tunity of seeing the flower; the fruit is somewhat fleshy, andcontains one or sometimes two nuts. When incisions are madeinto the trunk, it discharges abundantly a glutinous milk, mode-rately thick, without any acridness, and exhaling an agreeablebalsamic odour. The travellers drank considerable quantities ofit without experiencing any injurious effects; its viscidity onlyrendering it rather unpleasant. The superintendent of the plant-ation assured them that the negroes acquire flesh during the
* Abridged from an essay in Ann. de Chim. for Feb. 1818, which is an extractfrom a memoir read to the Academy of Sciences.
|116|season in which the cow-tree yields the greatest quantity ofmilk.
When this fluid is exposed to the air, perhaps, in consequenceof the absorption of the oxygen of the atmosphere, its surfacebecomes covered with membranes of a substance that appearsto be of a decided animal nature, yellowish, thready, and of acheesy consistence. These membranes, when separated fromthe more aqueous part of the fluid, are almost as elastic ascaoutchouc; but at the same time they are as much disposed tobecome putrid as gelatine. The natives give the name of cheeseto the coagulum, which is separated by the contact of the air;in the course of five or six days it becomes sour. The milk,kept for some time in a corked phial, had deposited a littlecoagulum, and still exhaled its balsamic odour. If the recentjuice be mixed with cold water, the coagulum is formed in smallquantity only; but the separation of the viscid membranes occurswhen it is placed in contact with nitric acid. This remarkable tree seems to be peculiar to the Cordillieredu Littoral, especially from Barbula to the lake of Maracaybo.There are likewise some traces of it near the village of SanMateo; and, according to the account of M. Bredmeyer, in thevalley of Caucagua, three days’ journey to the east of theCaraccas. This naturalist has likewise described the vegetablemilk of the cow tree as possessing an agreeable flavour and anaromatic odour: the natives of Caucagua call it the milk tree. M. Humboldt offers some general observations upon the milkyjuices of plants, and concludes with some particular observationsupon the fluid which is procured from the carica papaya;this has been analyzed by M. Vauquelin;* but the specimenwhich he examined had had its properties altered by havingbeen conveyed to a great distance, and kept for a long time. The younger is the fruit of the papaw, the more milk does ityield; in proportion as the fruit ripens, the milk, which is lessabundant, becomes more watery: there is then less of thatanimal matter which is coagulable by acids and by the absorp-tion of oxygen. When nitric acid is poured drop by drop intothe milky juice procured from a very young fruit, a very extraor-dinary phenomenon is observed. In the centre of each dropthere is formed a gelatinous pellicule, divided by greyish striæ;these striæ are merely the juice which is rendered more watery,because the contact of the acid has caused it to lose its albumen.At the same time the centre of the pellicule becomes opaque,and of the colour of the yolk of the egg; while it increases inbulk by the prolongation of the diverging fibres. The wholefluid at first has the appearance of an agate with milky clouds;and it appears as if organic membranes were produced under the
* Ann. de Chim. xliii. 267.
|117|eye. When the coagulum is moved, it becomes granulated likesoft cheese; the yellow colour is reproduced by adding a fewmore drops of nitric acid. The acid in this case acts in thesame manner with the oxygen of the atmosphere, at the temper-ature of from 80·5 to 95° (Far.); for the white coagulumbecomes yellow in two or three minutes by exposure to the sun.After some hours, the yellow colour turns brown, undoubtedlybecause the carbon is more liberated in proportion as thehydrogen, with which it was combined, is burned. The coagu-lum formed by the acid becomes viscid, and acquires the waxyodour, which is perceived when the muscular fibre or fungi aretreated with nitric acid. From the interesting experiments ofMr. Hatchett, it may be supposed that in this case the albumenis partially converted to the state of gelatine.
When the coagulum of the papaw is thrown into water, itsoftens, becomes partially dissolved, and gives the water ayellowish tinge; the milk, when placed in contact with water,also forms membranes; a tremulous jelly, similar to starch, isimmediately precipitated, and the appearance is more remark-able if we employ water at the temperature of from about 100°to 140° (Far.). If carbonate of soda be added to the fluid, thecoagulum is not formed; but it is immediately produced by the ad-dition of an acid. If we compare together the milky juices of thepapaw, the cow tree, and the hævea caoutchouc, we find a strik-ing resemblance between the juices which abound in caseousmatter, and those in which the caoutchouc predominates.According to the opinion of M. Gay-Lussac, we may considerthe caoutchouc as analogous to the oily part or the butter of thevegetable milk; in the vegetable milk we find caseum and caout-chouc; in animal milk, caseum and butter. The albuminous andthe oily principles exist in different proportions in the differentspecies of animals and milky plants; and in the last, they arefrequently united to other substances which render them injuriousas articles of food.