Popular Science Monthly/Volume 71/September 1907/A Scientific Comedy of Errors
|A SCIENTIFIC COMEDY OF ERRORS|
UNIVERSITY OF COLORADO
THE scientific man of any period, if he will examine the work of his predecessors, may be comforted or discouraged, according to his point of view. It is in the highest degree encouraging to note the steady and rapid progress of science during the last two hundred years and more. It is flattering to the vanity of us moderns to realize that we stand on the very apex of the pyramid of knowledge which the human race has erected at the cost of so much toil, and can look down with indulgent contempt on the comparative ignorance of earlier generations. How stupid they were! How little they knew!—but we—well, there really never has been anything so superior. There is, however, an ancient story about a monkey which climbed a pole and for every three feet he climbed he slipped down two. Was the animal, after all, certainly a monkey? Is there no similarity between his progress and that of the human race? If the science of the past reads to us to-day like a comedy of errors, is it perfectly certain that our productions will not so appear to that hateful body of supercilious critics, our posterity? On second thought, there may be in the history of human learning as much cause for modesty as for exultation. As a tangible case in point we present a summary of the early history of the cochineal and allied dye-producing insects, and more particularly of a forgotten pamphlet by one Frederic Friedel, whereby he earned the degree of doctor of philosophy at the University of Leipzig, in 1701. For his time, Friedel was a man of unusual wisdom, filled with the true spirit of science, so much so that he was not afraid to tilt against the greatest of biological authorities then living, and, in so doing, came out with a flying pennant. Yet, in the light of modern knowledge, it appears that he corrected the blunders of Leeuwenhoek only to make somewhat lesser ones of his own; not, however, through lack of care or lack of sense, but from the unavoidable imperfection of his knowledge.From very early times, it was customary to utilize the coloring matter obtainable from certain small round objects to be found on various species of oaks in the region of the Mediterranean. Dioscorides and other authors report their occurrence in Galatia, Armenia, Cicilia, Spain, Portugal and Sardinia: in later times they have been known in the south of France, Crete and Syria; while the north of Africa has furnished a less valuable kind. To Theophrastus they were known
as the κὀκκος φοινικὀς, while in later times the name Kermès, from the Arabic, came into general use.
For many centuries the nature of the Kermes remained uncertain. To all appearances it was a berry, and the opinion that it was of purely vegetable origin prevailed. However, it appears that Quinqueran de Beaujeu, as early as 1551, published a book on the productions of Provence, entitled De laudibus Gallo-Provinciæ, in which he clearly indicated that the Kermes was an insect, and described its transformations. The supposed berries, says he, are the mothers, who presently have families of innumerable very minute worms. These latter locate upon the twigs at various points, increase in size, and at length look no longer like animals, but peas.
Planchon, to whom we are indebted for the reference to Quinqueran, goes on to remark that it is curious that after these observations had been published, many intelligent writers showed hopeless confusion upon the subject. In particular, it had been observed that from the Kermes sometimes issued small four-winged insects not unlike those coming from the oak-apples or galls. Hence it was concluded that the Kermes must be a sort of plant gall, wholly made up of vegetable tissue, but nourishing an insect. We know now, of course, that the four-winged insects were merely parasites of the Kermes, which lived as minute maggots within its body, destroying it and finally issuing as adult flies.
With the discovery of Mexico, things took on a new turn. Francisco Hernandez and others reported that on the tuna, or prickly pear, of that country there grew a new sort of coccus, which was much to be preferred to the one found upon the oak, or to the scarlet grain found upon the roots of plants in Poland.
This new coccus, which came to be known as the cochinilla, or cochineal, was largely imported into Europe; and eventually the cacti were brought over, and grown in Algeria, Madeira, etc., so that the dye-material could be produced nearer the market. With the impetus thus given to the study of coccus—or, as we should now say, the Coccidæ—the question as to the true nature of the material pressed anew for settlement. According to the "Encyclopædia Britannica," the idea that the cochineal was the seed or fruit of a plant was prevalent as late as 1725, but Martin Lister, in 1672, indicated its relation to the insects. In 1703, it is stated, Leeuwenhoek discovered its true nature by the aid of the microscope, "but not unnaturally supposed it to be allied to the ladybird."
This statement of the case, however, is not quite exact. We have before us a little pamphlet published as early as March, 1701, the precise date, according to a penciled figure, being the fourteenth of that month. This work is a thesis for the degree of doctor of philosophy, presented to the University of Leipzig by Frederic Friedel, and is entitled Dissertatio Physica de Cochinilla. In it, the whole question of the nature of the cochineal is fully discussed, with copious references to previous authors and many original observations.
The work consists of six chapters; the first on the name of the cochineal; the second on its habitat and the plants infested, with some interesting information on the different kinds of cacti; the third on various opinions concerning the nature of the cochineal; the fourth giving the details of the author's views as to its nature; the fifth on its culture and the methods of collecting it; and the last on its different varieties and its uses. The whole treatise is, of course, in Latin, but we give a free translation of the parts with which we are particularly concerned, abbreviating here and there.
After giving a general summary of the hitherto recorded observations and opinions. Dr. Friedel proceeds:
different languages, bringing out the fact that these creatures are dedicated to Our Lady, the Virgin Mary, or in other cases to God, for reasons not explained. In France they are called God's horses, Chevaux de Dieu, in England ladybirds or cowladies, and so forth.
To these familiar ladybirds,
The modern entomologist begins to wonder what all this has to do with the cochineal, which is by no means a beetle, though truly an insect, but the author proceeds:
With this description, aided by an excellent figure given in the one plate which ornaments the pamphlet, we are able without difficulty to explain the mystery. The American beetle is the Chilocorus cacti, a genuine ladybird, which does indeed live upon the tuna among the cochineal insects, feeding upon them. When the latter are gathered, the beetles are often carried with them, and Friedel, examining the dried grains, naturally found the specimens he describes. In 1701 not much was known about the classification of insects, and it never occurred to him that a creature like the cochineal, which we now know to have a sucking mouth, could not be related to a beetle.
Yet, aware that scoffers exist, the author is constrained to proceed:
Friedel then proceeds to combat an opinion, which he attributes to Leeuwenhoek and an anonymous Spaniard mentioned in the English Transactions (of the Royal Society) No. 193, to the effect that the cochineal is a portion of the adult American ladybird—the Chilocorus cacti.
What an excellent argument! It is proven beyond doubt that the cochineal is no part of the ladybird, notwithstanding the assertions of the most eminent authority then living. We have no fault to find with particulars given, except that the little prominences on the cochineal, where the legs were hereafter expected to appear, were in reality the bases of the minute legs of that insect.
Returning now to the constructive argument, the author gives his conclusion that the cochineal must be derived from the aforesaid beetles, and yet is not any part of them. The simple explanation is that the cochineal, when mature, transforms into a beetle, and in doing so utterly loses the power of staining, and hence is no longer to be termed a cochineal. Now this loss of color at maturity is paralleled by other phenomena already recorded. In the case of the dye-coccus of the oak, the Kermes, so long as the little berries are full of little worms or animals, they are rich in the colored juice. After a while, when the little worms [the larvae of the Kermes, in reality] are called by the heat of the sun from their sacs [that is, the bodies of their mothers] they can be destroyed by the pressure of the hand, and forced into a mass which is appropriately termed vermillion. Otherwise, before the exclusion of the worms, the dried berries will equally preserve the desired color. It is just the same in the coccus polonicus [Margarodes polonicus of modern entomologists], which is said to cling to the roots of several herbs. These little bodies at a stated time turn into little winged insects, as is stated by several authors, including Martin Bernhard in his description of the Royal Garden of Varsovie. As soon as these insects [probably males of the Margarodes] fly away, they are manifestly deprived of all color, and not only this, but the cortex which is left retains nothing of the precious coloration.
So, says Friedel, since in all these different sorts of coccus the red color disappears in the last stage, when the creature is transformed into a fly or some other little animal, it is easy to understand why the beetles produced from the cochineal show no red pigment. The point is important, because it is necessary that the cochineal should be collected in time, before its last transformation, and while it is still swollen with the juice.
The analogy is here not very convincing, since the Kermes does not turn into a single insect, but produces a multitude of "worms," as Friedel clearly states. It seemed sufficient to him, however, and he never got a glimpse of the true fact that the cochineal insects do indeed turn into the beetles, in the same manner that the lamb may be said, under suitable circumstances, to be transformed into the lion.
Assuming that the cochineal was the pupa of the beetle, it remained to fortify this conclusion by still other arguments. In the first place, Herrera and Laetus had given some slight account of the development of the cochineal, from actual observation. From this it might be gathered that there was at first a minute or mite-like insect, which developed into the cochineal-grain. This accords very well, so far as it goes, with what was to be expected according to the theory. "That grain is covered on the outside by a certain thin tunic, which contains shut up within it the little animal, which is soon to be transformed into a beetle"—this is, however, an inference of Friedel's, not of Herrera's.
"But," says Friedel, "for a more beautiful illustration of my hypothesis, I thought T might describe the transformation of the European ladybird, which is certainly sufficiently allied to the American to permit accurate deductions to be drawn from it." So he went first to the book on insects by John Goedart "that very illustrious painter of Middleton," a work which several years back Martin Lister had published in a new and revised edition. In this work, p. 274, it appeared that first from little blackish eggs deposited in a sort of circle on the leaves of the Ribes [currant or gooseberry], there sprang, "from the nurturing of the summer air," little animals, which immediately after hatching could scarcely move, until after an interval of several days they learned to creep a little, and finally to run about freely. These insects were subsequently observed to shed their skins, like serpents, as they increased in size, and this was done four distinct times, and last they obtained the final red skin, variegated with black spots. To these statements the author added that as often as these beetles stripped themselves of their skins, they fixed their feet firmly in the place they occupied, and crept out, leaving the empty skin in its natural form, so that at the first glance you would swear the little animal was still standing there."Now," says Friedel, "As I read this, it can scarcely be told how saddened I was, for the hope I had previously conceived was falling into ruin." The account of Gœdart did not really seem to confirm the hypothesis about the cochineal, for there was no description of.any stage that really corresponded to the grain. Friedel was about to change his opinion in toto, when he "had another seasonable suggestion from the most excellent Dr. Lang, to whose most faithful training I owe almost everything in the course of my medical studies." For as Dr. Lang was the first to suggest to Friedel the theory about the nature of the cochineal which formed the subject of this thesis, so he now came to the rescue with facts and experiments concerning the German ladybird "depicted as in life with an elegant brush in colors, and most accurately noted from day to day," all of which, in the year just passed, Friedel was permitted to observe and confirm with his own eyes.
This is really an excellent account of the ladybird, excepting only the error as to its food, and from these observations Friedel felt encouraged to believe that he had put the finishing touches on his theory of the cochineal; for was not the ladybird pupa just like it? "But," says he, "if perchance this should still seem doubtful, here is a further observation to confirm it. When a friend, addicted to trade, gave me at one time a large enough heap of cochineal to examine, I found mixed with, it several worms, not yet altogether changed into pupæ, of a color which from ashen was becoming purple, and which when immersed for a while in water, assumed the form seen in the engraving under the letter C. Hence there came to me the suspicion that under this form appeared the worm of the cochineal before giving itself to rest; for that it certainly belongs to this family, I am persuaded by the purple color which it discharges into the water in which it is immersed, just like the cochineal itself. For when all the eggs of these insects are not hatched in one precise day it at least becomes probable that neither are all these worms in one moment transformed into pupae, or the beetles simultaneously creep forth from these. So, without doubt, when the harvest of pupæ is at hand, several of these worms, which have not yet reached the pupa state, and also several adult beetles, are shaken off at the same time from the tuna. Consequently, we usually find them all mixed, in more or less abundance, with the best cochineal." The worms thus found may be the true larvæ of the ladybeetle, or in other cases, the larvæ of certain two-winged flies of the family Syrphidæ, which also prey upon the cochineal. The presence of the flies is especially indicated by another observation of Friedel's—that he found even a few cup-shaped objects, in which were occasionally seen some small grains of cochineal. Here, he thought, were actually the skins left empty after the exit of the beetles; but on further reflection he abandoned the idea, as they really were not large enough to hold the beetle. The grains found in them were very minute, and were doubtless only cochineal larvæ which had wandered in by accident; and finally, some of these cups still contained, not a beetle, but a single fly. These were, we may now rest assured, the puparia of a predatory Dipterous insect, either a Syrphid or a species of Leucopis.
By the time of Linnaeus, some fifty years later, it was clearly known that the cochineal had nothing to do with the beetles, but belonged to the Hemiptera. Even then, however, it seemed fated to be a source of error and misunderstanding. When Linnaeus was preparing his great "Systema Naturæ," a friend of his, Daniel Rolander, resident in the "West Indies, sent him what he supposed to be unusually fine specimens of the cochineal alive on a piece of cactus. Linnæus naturally used these in making his description of the Coccus casti, and until 1899 nobody seems to have suspected that they were not the real cochineal. However, Rolander sent some at the same time to DeGeer, who figured them, and from the account he gives, and indeed also from that of Linnæus, it is evident that the Coccus cacti L. is no cochineal, but a species of a quite different subfamily, which, curiously, has never been found by any entomologist since it was discovered by Rolander.