On the Cow Tree of the Caraccas, and on the Milk of Vegetables in general.

Extracted from a Memoir on this Subject, by A. de Humboldt.

From the Annales de Chimie et de Physique.

We had for several weeks (says M. Humboldt) heard speak of a tree growing in the vallies of Aragua, whose juice was a nutritive milk, and hence called the cow tree, palo de vaca; and we were assured that the negroes of the farm, who drank abundantly of this milk, consider it as a very wholesome food.

As all the milky juices of plants hitherto known were either acrid or bitter, and more or less poisonous, this assertion appeared to us extraordinary; but experience has shewn us, during our stay at Barbula, (a province of the Caraccas,) that the virtues of the palo de vaca had not been exaggerated.

This beautiful tree has the appearance of the chrysophyllum caimita: its leaves are oblong, pointed at the extremities, coriaceous and alternate, and are marked with lateral ribs, raised from below the leaf, and parallel; their length is about ten inches.

We did not see the blossom: the fruit is somewhat fleshy, and contains one and sometimes two nuts.

When incisions are made in the trunk of the tree, it gives an abundance of thick glutinous milk, not at all acrid, and which exhales an agreeable smell of balsam.

We drank it out of calebash shells, in considerable quantity, both night and morning, without finding any unpleasant effects from it.

The clamminess alone made it a little disagreeable.

The negroes and free servants of the plantations dip their manioc and cassava bread in it: and the overseer assured us, that the slaves become sensibly fatter in the season in which the palo de vaca yields the most milk.

When exposed to the air this milk becomes covered, perhaps owing to the absorption of oxygen, 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 elastic, almost like caoutchouc; but after a time they putrefy like gelatine.

The common people give the name of cheese to the coagulum which separates from this milk by the contact of air: this cheese grows sour in five or six days.

When the milk was enclosed in a corked bottle it deposited a little coagulum, but far from becoming offensive, it exhaled a balsamic smell.

The fresh juice mixed with cold water would hardly coagulate, but the viscous membranes separated on the addition of nitric acid.

The extraordinary tree of which we are speaking, appears to be peculiar to the cordillera du littoral, particularly from Barbula to the lake of Macaraibo.

Some stems of it are also to be found near the village of San Mateo, and, according to Mr. Bredmeyer, whose travels have so much enriched the gardens of Schonbrunn and Vienna, it is met with the valley of Caucagna, three days journey east of Caracca.

This naturalist has found, as we have, this vegetable juice to be of an agreeable taste, and an aromatic smell.

The natives call the tree Arbol de Leche, Milk Tree.

Long before chemists had detected small portions of wax in the pollen of flowers, the varnish of leaves, and the white efflorescence on our plums and grapes, the inhabitants of the Andes of Quindiu made candles of the thick coating of wax which covers the stems of the palm trees.

It is but a few years since the caseum, the basis of cheese, has been discovered in almond emulsion; and yet, for centuries, in the mountains near Venzuela, the milk of a tree, and the cheese separating from this milk, have been regarded as a salutary food.

What can be the reason of this singular order in the developement of knowledge?

How have the common people of one hemisphere made discoveries which have so long eluded the sagacity of skilful and enlightened chemists in the other?

It is, because but a small number of elements and principles, differently combined, are unequally distributed in different families of plants; and because people that derive almost all their food from the vegetable kingdom, detect farinaceous and nutritious matter wherever nature has 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 Manioc, united to an acrid and sometimes venomous juice.

Hence the untutored native of America, and of the South Sea Isles, has learnt to dulcify the feculum, by pressing out and separating the juice.

In the milk and milky emulsions of plants, substances eminently nutritious, such as albumen, caseum, and sugar, are mixed with caoutchouc and acrid deleterious principles, such as morphine and hydro-cyanic acid.

I shall add the results of some experiments which I made on the juice of the papaw (Carica papaya) during my residence in the vallies of Aragua, though I was then almost entirely deprived of chemical re-agents.

The same juice has been since examined by Vauquelin; and this eminent chemist has fully detected the presence of albumen and casiform matter: he has compared the milky juice of the papaw to a strongly animalised substance, like the blood of animals; but he could only examine a juice that had fermented and formed a fetid coagulum during the voyage from the Isle of France to Havre; and he expressed the wish that the papaw juice could be examined as soon as it had flowed from the fruit stem.

The younger the fruit is, the more abundant is its juice: it is even found in the germ before fecundation.

As the fruit ripens, the milk diminishes in quantity, and becomes more watery; and contains less of this animal matter, which is coagulable by acids, and by exposure to air.

As the whole fruit is viscous, it may be presumed that in proportion as it becomes larger, the coagulable matter is deposited in its organs, and contributes to form the pulp, or the fleshy portion.

When nitric acid, diluted with four parts of water, is poured drop by drop into the expressed juice of a very young fruit, a singular appearance is observed: there forms in the centre of each drop a gelatinous pellicle, divided by grey striae.

These striae are only the juice, rendered more watery by the contact of the acid which has separated its albumen.

At the same time the centre of each pellicle becomes opake and yellow, like the yolk of an egg, and these pellicles gradually enlarge, as if by the prolongation of diverging fibres.

All the liquid at first has the aspect of clouded agate, and the organic membranes appear to shoot up under the eye.

When the coagulum extends over the whole mass, the yellow spots again disappear, and on stirring the liquid it becomes granulated like soft cheese.

The yellow re-appears on adding fresh nitric acid.

The acid here has the same action as the contact of atmospherical oxygen at a moderate temperature, for the white coagulum becomes yellow in two or three minutes when exposed to the sun.

In some hours more the yellow colour passes into shades of brown, doubtless because the carbon becomes more free in proportion as the hydrogen with which it was united undergoes combustion.

The coagulum by nitric acid becomes viscous, and takes that peculiar waxy smell which I have observed before in treating the fleshy part of truffles with nitric acid.

Mr. Hatchett's interesting experiments would lead me to suppose that the albumen is partly converted to gelatine.

The fresh coagulum of the papaw softens in water, is partly dissolved, and tinges the liquid yellow.

The milky juice, put in contact with water, forms also these membranes, and there immediately falls down a sparkling jelly, like starch.

This appearance is still more striking if the water is heated from 100° to 140° Fahrenheit.

The jelly is more condensed as the water added is greater.

It long preserves its whiteness, and only becomes yellow by nitric acid.

In imitation of Fourcroy and Vauquelin's experiment on the juice of the hevea, I added to a solution of papaw milk some carbonate of soda.

No coagulum was formed, and the membranes only appeared when the excess of soda was neutralised, or more than neutralised by an acid.

In the same manner I dispersed the coagulum formed by nitric acid, by lemon-juice, or by hot water; and mixing it with carbonate of soda, the juice becomes again milky as in its original state, but this experiment succeeds only when the coagulum has been recently formed.

In comparing the milky juices of the papaw, the palo de vaca, and the hevea, one may see a striking analogy between the juices that contain casiform matter, and those in which caoutchouc predominates.

All the white fresh preparations of caoutchouc, as well as the waterproof cloaks made in Spanish America, by covering the cloth on each side with the caoutchouc juice, exhale a nauseous animal odour.

This seems to shew that caoutchouc in coagulating carries with it the caseum, which is perhaps only albumen a little altered.

The bread-fruit is no more identical with bread than are the bananas before maturity, or the tuberous and amylaceous roots of the manioc, the dioscoreae, the convolvulus batatas, and the potatoe.

On the other hand, the milk of the cow-tree contains real casiform matter, like the milk of the mammiferae.

Speaking in general terms therefore, we may, with Gay-Lussac, consider the caoutchouc as the oily principle, or the butter of vegetable milk, the latter containing caseum and caoutchouc, as animal milk holds caseum and butter.

These two principles differ in their respective proportions, both in the animal and vegetable milks.

With the latter are often also mixed other principles, noxious as food, but which may perhaps come to be separated by chemical means.

Every vegetable milk becomes more fitted to be the food of man, in proportion as it is deprived of acrid and narcotic principles, and as the casiform matter predominates over the caoutchouc.