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further towards the centre, than any thing in the world besides, and yet we are told that the sea is no where above a German mile deep, which is almost nothing in comparison with the semidiameter of the earth as specified above. But how are matters circumstanced in the great deeps? not at all favourably for the hypothesis of a central fire; there are no plants, nor any fish, those regions being too cold, as say the philosophers, for the spawn of fish to quicken there.

But perhaps authority swayed most, and the moderns founded their notion on the ancient Tartarus. This I fear is a misapprehension, for Hesiod places it under and not in the middle of the earth, * and accordingly our Milton has judiciously seated it far without this terraqueous globe.

These observations, Mr. Urban, are very superficial, and are only thrown out in order to induce some able hand to give this question, which certainly merits it, a thorough discussion, and it would give me great pleasure, as I dare say it would you, to see it undertaken by some adequate pen.

I am, Sir,

Your most obedient, 1753, Feb.

Paul GEMSEGE.

XII. History and Culture of Cochineal.

COCHINEAL is greatly esteemed throughout Europe for the richness and excellence of its die; it has hitherto been produced only in the Spanish West Indies, but our newspapers tell us, that an attempt is now making to produce it in Spain, and as the nature and origin of it are not very generally *known, it is hoped the following particular and authentic account of it will not be unacceptable to the public.

Yours,

AN.

It was not long ago believed that Cochineal was the seed of a plant; an opinion which probably took its rise from the circumstances of its being found upon, and gathered from, the leaves of a West Indian shrub: bnt certain it is that Cochineal belongs to the animal, and not to the vegetable,

* Hesiod. Oscyor. 720, 721, et M. L Clerc ad. v. 708,

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kingdom. The grains of Cochineal are each of them a little animal, which, when alive, greatly resembles a wood-louse, and from this resemblance it takes its name; for the Spaniards who first brought it into Europe and gave it its name, call a a wood-louse, Cochinilla. These animals do not indeed roll themselves up, on being touched, as the wood-lice do, nor are the largest of them bigger than a sheep-tick.

The plant, or shrub, whereon these little animals are bred, nourished, and brought to perfection, is called, in the West Indies, Nopal, or Nopalera, and is a sort of fig-tree. It is indeed rather'a heap of leaves than a shrub. After the trunk or stem has risen a little above the ground, it divides itself into several arms or branches, and the trunk itself and its several ramifications are full of knots: each of these knots sends out a leaf, and from the end of that leaf springs another, and so on till the plant arrives at its full growth. Those leaves which spring first and are nearest the trunk or branches, are the largest: the leaves are pretty long and not flat, but somewhat rounded, or convex, and full of little portuberances, and covered with a thin and delicate membrane which always preserves a lively green colour. Its flower is small, and like a flesh-coloured ball, in the centre of which appears the fig; and as the fig increases, the flower decays and loses its colour, till at last it falls and leaves the fig alone. When the fig is ripe, its outer skin, or husk, is white, but its pulp or substance

is of a deep red: it is very wholesome and pleasant to the taste, but it tinges the urine of those that eat it, and makes it look like blood, a circumstance which has often given great uneasiness to those who were ignorant of this property of the fruit.

The nopal is propagated thus : a number of holes are made in a line, about half a yard deep, and about two yards distant from each other: in every hole is put one or two leaves of the nopal well spread and stretched out, and then covered up with earth, and from each hole there springs a new plant. The grounds in which it is cultivated ought to be well weeded and kept clear of all other herbs whatever; for they deprive it of its due nourishment.

The plants should be pruned soon after the Cochineal is gathered, and all superfluous leaves cut away: they will put out fresh leaves the following year, and by these means will become more strong and vigorous. But it is to be observed that the Cochinillas which feed upon young plants, are larger and of a better quality than those which are gathered from plants which have stood some years.

The Cochinillas live upon the leaves of the nopal, and are

fed and nourished by sucking their juice. The juice of the leaves is watry and colourless, but these animals in converting it into their own substance, change it to a fine crimson colour. One thing very remarkable is, that the Cochinillas do not gnaw nor devour the substance of the leaves, nor do the leaves suffer the least perceivable hurt or injury by their feeding upon them. It is probable that the little animals only suck the grossest juices through the pores of the thin membrane which covers the leaves.

When the Cochinillas are come to their full growth, they gather them into earthen pots, close stopped, that they may not creep out; and soon after they kill them in order to prepare them for sale. The Indians have three different ways of killing them, viz. By hot water, by the fire, or by exposing them to the heat of the sun. From these different methods there arises a great variety in the colour of Cochineal, some grains being of a brighter and much better colour than others. But whichsoever of these three methods is pursued, there is a proper degree of heat which must be carefully observed: when water is used, a sufficient quantity duly heated is sprinkled upon them: they who kill them by fire, put them into ovens properly heated : but the best Cochineal is that which is prepared by the heat of the sun.

In order to have the Cochineal in its utmost perfection, it is not only necessary to choose the best method of killing and preparing the Cochinillas, but also to know the right time for gathering them off the leaves of the nopal; but the knowledge of this is only to be attained by practice and experience, and no certain rule can be established for it: and it is observed that the Cochineal of the several provinces of the West Indies is better or worse, just as the Indians employed about it are more or less skilful and experienced.

The Cochinillas in several particulars may be compared to the silk worms, and especially in the manner of laying their eggs. Such of them as are destined to breed, are taken from the leaves of the nopal when they are in full vigour, and put into baskets well closed and lined with linen, close. wrought and folded several times, that none may be lost; there they lay their eggs and soon after die. The baskets must be kept close covered up till the proper season of the year arrives for laying the Cochinillas upon the leaves of the nopalera. The time proper for laying them upon the leaves is in the month of May or June, when the nopalera is in its prime: and when about this time the baskets are opened, the Cochinillas appear about the size of small mites, and by observing them attentively you may just perceive them move.

In this state they scatter them upon the leaves of the plants: a ben's egg shell full of them is sufficient to furnish a whole plant.

There are several things either very pernicious, or fatal to the Cochinillas. If strong northerly winds come on soon after they are laid upon the leaves, they are all destroyed. Rains, snow, mists, and frosts, often kill them, and at the same tinie blast the leaves of the nopalera. The only remedy in these cases is to warm and smoke them. Hens and some small birds eat the Cochinillas, and so do several sorts of worms and insects, which breed in the places where the nopaleras grow. Great care therefore is taken to keep off the birds, and to destroy the reptiles and insects which are prejudicial to them.

The Cochinillas are bred in the provinces of Ooxaca, Flascala, Chulula, New Galicia, and Chiapa, in the kingdom of New Spain, and also in the provinces of Hambato, Loja, and Tucuman in Peru. But although the Cochinillas and nopaleras abound in all these provinces, yet they are not properly managed and prepared for sale in any but that of Doxaca, and there only do the Indians make it their business to cultivate and take care of them: in all the others the nopaleras are wild and uncultivated, and the Cochinillas breed of themselves without being looked after, and therefore the Cochineal gathered in these provinces is much inferior in goodness to that of Ooxaca: not that the nopaleras or Cochi-, nillas are of a worse kind, but because they are not properly managed and cultivated.

In the kingdom of Andalysia in Old Spain, there is a plant called Tuna, which very much resembles the nopal, and bears a fruit like it. It only differs from the nopal in respect of its leaves, which are broad and flat and full of prickles of different sizes. It is therefore thought that the tuna will be as proper food for the Cochinillas as the nopal : and as the climate of Andalusia is dry and temperate, and agreeable to the Cochinillas, the attempt to breed them there will probably nieet with success.

1753, Feb.

XIII. Experiments on Animal Digestion.

MODERN naturalists and physicians rest the business of digestion on these two queries ; 1. Is it the work of trituration

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alone? 2. Is it brought about by the joint operations of trituration and dissolvents? Experiments alone must settle the controversy; and birds, I think, for many reasons, are, of all animal subjects, by far the properest to try them upon.

The structure of the stomach in birds, is as various as their outward form. In some it is very fleshy, thick, and of a close texture, called a gizzard; in others very thin, thougla of a much larger capacity, in proportion to the body, being a sort of membranous pouch: in some, the stomach is partitioned into gizzard, and membrane; and lastly in others it is all over of a middle texture and thickness, between the one and the other.

The gizzard is the stomach which seems the most favourable to the system of trituration. Its thickness, solidity, and compact texture, lead us to think it destined to act with a mighty force; and birds that have it are known to swallow sand, gravel, and small flints, with other little stones, some of which are always found within them. Such stomachs therefore seem fitted as mills for grinding and braying the grain they eat for food. The experiments of the Florentine Academy, repeated by Redi and Borelli, have further con, firmed this plausible notion. Hollow particles of glass, which they gave to chickens, ducks and turkeys, were found reduced to a fine powder. However Valisnieri, famous for a multitude of fine observations in natural history, and ever ready to oppose popular prejudices, could not rest satisfied with these facts. He looked upon the resemblance between a stomach and a mill as chimerical; he could not but think, with a great many others, that a stomach thus capable of grinding corn, must also grind itself away. He considered the reduction of glass to powder as the effect of a powerful dissolvent, and found proofs thereof in the stomach of an ostrich, which he judged incontestable. I shall name one in particular; he there met with bits of glass perforated with a vast number of holes more minute than those of the finest silver-wire plates,

Having myself experienced how easily small glass beads of various sizes and shapes were powdered, without at all excoriating the gizzard, I caused chickens, ducks, and turkeys to swallow short tubes of glass, which were about five lines in length, and four in diameter, of which the bore was about two lines. These, after the death of the fowls, I found no longer to retain their former shape, for they were all split asunder lengthwise. They had resisted the pressure which acted upon them inwards, from without, which must have been prodigious to have broken them; but they yielded

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