Catholic Churchmen in Science Part 6

[Ill.u.s.tration: NICOLAUS STENONIS]

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VI.

BISHOP STENSEN, ANATOMIST AND FATHER OF GEOLOGY.

In the sketch of the life of Father Athanasius Kircher, the distinguished Jesuit scientist, mathematician, and Orientalist, I called attention to the fact that, at the very time when Galileo was tried and condemned at Rome, because of his abuse of Scripture for the demonstration of scientific thesis, a condemnation which has been often since proclaimed to be due to the Church's intolerant opposition to science, the ecclesiastical authorities at Rome invited Father Kircher, who was at that time teaching mathematics in Germany, to come to Rome, and during the next half-century encouraged him in every way in the cultivation of all the physical sciences of the times. It was to popes and cardinals, as well as to influential members of his own order of the Jesuits, that Father Kircher owed his opportunities for the foundation of a complete and magnificent museum, ill.u.s.trating many phases of natural science--the first of its kind in the world, and which yet continues to be one of the noteworthy collections.

During the decade in which the condemnation of Galileo and the invitation of Father Kircher to Rome took place, there was born, at {138} Copenhagen, a man whose career of distinction in science was to prove even more effectively than that of Kircher, if possible, that there was no opposition in ecclesiastical circles in Italy, during this century, to the development of natural science even in departments in respect to which the Church has, over and over again, been said to be specially intolerant. This scientist was Nicholas Stensen, the discoverer of the duct of the parotid gland, which conducts saliva into the mouth, and the founder, in the truest sense of the word, of the modern science of geology. Stensen's discovery of the duct which has since borne his name was due to no mere accident; for he was one of the really great anatomists of all time, and one distinguished particularly for his powers of original observation and investigation. To have the two distinctions, then, of a leader in anatomy and a founder in geology, stamps him as one of the supreme scientific geniuses of all time, a man not only of a fruitfully inquiring disposition of mind, but also one who possessed a very definite realization of how important for the cause of scientific truth is the necessity of testing all ideas with regard to things physical, by actual observations of nature and by drawing conclusions not wider than the observed facts.

Notwithstanding this characteristically scientific temper of mind, which, according to most modern ideas, at least, would seem to be sure to lead him away from religious truth, Stensen at the {139} very height of his career as a scientist, while studying anatomy and geology in Italy, became a convert from Lutheranism, in which he had been born, to Catholicity, and thereafter made it one of the prime objects of his life to bring as many others as possible of the separated brethren into the fold of the Church. When he accepted the professors.h.i.+p of anatomy at the University of Copenhagen, it was with the definite idea that he might be able to use the influence of his position to make people realize how much of religious truth there was in the old Church from which they had been separated in the preceding century. After a time, however, his zeal led him to resign his position, and ask to be made a priest, in order that he might be able more effectively to fulfil what he now considered the main purpose of his life, the winning of souls to the Church. As, since his conversion, he had given every evidence of the most sincere piety and humble simplicity, his desires were granted. His book on geology, however, was partly written during the very time when he was preparing for sacred orders, and was warmly welcomed by all his Catholic friends. After spending some time as a missionary, and attracting a great deal of attention by his devout life and by the many friends and converts he succeeded in making, the recently converted Duke of Hanover asked that the zealous Danish convert should be made bishop of his capital city. This request was immediately granted, and Stensen spent several years {140} in the hardest missionary labor in his new field. As a matter of fact, his labors proved too much for his rather delicate const.i.tution, and he died at the comparatively early age of forty-eight. The visitor to the University of Copenhagen marvels to find among the portraits of her professors of anatomy one in the robes of a Roman Catholic bishop. This is Stensen. In 1881, when the International Geographical Congress met at Bologna, it adjourned at the end of the session to Florence to unveil a bust of Stensen, over his tomb there. Here evidently is a man whose life is well worth studying, because of all that it means for the history of his time.

Nicholas Stensen--or, as he is often called, Steno, because this is the Latin form of his name, and Latin was practically exclusively used, during his age, in scientific circles all over Europe--was born 20 January, 1638, in Copenhagen. His father died while he was comparatively young, and his mother married again, both her husbands being goldsmiths in high repute for their skill, and both of them in rather well-to-do circ.u.mstances. His early education was obtained at Copenhagen, and the results displayed in his attainments show how well it must have been conducted. Later in life he spoke and wrote Latin very fluently and had, besides, a very thorough knowledge of Greek and of Hebrew. Of the modern languages, German, French, Italian, and Low Dutch he knew very well, mainly from residence in the various countries in which they {141} are spoken. A more unusual attainment at that time, and one showing the ardor of his thirst for knowledge, was an acquaintance with English. In early life he was especially fond of mathematics and, indeed, it was almost by accident that this did not become his chosen field of educational development.

At eighteen he became a student of the University of Copenhagen, and after some preliminary studies in philosophy and philology devoted himself mainly to medicine. At this time the Danish University was especially distinguished for its work in anatomy. The famous family of Bartholini, who had for several generations been teaching there, had proved a copious source of inspiration for the students in their department, and as a consequence original investigation of a high order, with enthusiasm for the development of anatomical science, had become the rule. The external situation was not favorable to learning, for Denmark was engaged in hara.s.sing and costly wars during a considerable portion of the seventeenth century; yet the work accomplished here was, undoubtedly, some of the best in Europe. Young Stensen had the advantage of having Thomas Bartholini as his preceptor, and soon, because of his enthusiasm for science, as friend and father.

Stensen had been at the University scarcely two years when the city of Copenhagen was besieged by the Swedes. Professor Lutz, of the University of St. Louis, who has recently written {142} an article on Stensen, which appeared in the _Medical Library and Historical Journal_ for July, 1904, says of this period:

A regiment of students numbering two hundred and sixty-six, called "the black coats" on account of their dark clothes, was formed for the defence of the city; upon its roster we find the name of young Steno. During the day they were at work mending the ramparts, and the nights were spent in repelling the attacks of the enemy. In the course of this long siege, the city was compelled to cope with a more formidable enemy than the Swedes--famine with all its horrors--before relief came in the shape of provisions and reinforcements furnished by the Dutch fleet. Throughout these turbulent days the student soldiers rendered valuable services to their country, and though it be true that "inter arma silent musae"--"the war G.o.ds do not favor the muses"--it appears nevertheless that Steno attended the lectures and dissections which were conducted by the teachers in the intervals when the student were not on duty.

After some three years spent at the University of Copenhagen, Stensen, as was the custom of the times, went to pursue his post-graduate studies in a foreign university. Bartholini furnished him with a letter of recommendation to Professor Blasius, who was teaching anatomy at Amsterdam in Holland. Amsterdam had become famous during the seventeenth century for the very practical character of its anatomical teaching. As the result of the cordial commendation of Bartholini, Stensen became an inmate of the house of Professor Blasius, and was given {143} special opportunities to pursue his anatomical studies for himself. He had been but a very short time at Amsterdam, when he made the discovery to which his name has ever since been attached, that of the duct of the parotid gland. Stensen's discovery was made while he was dissecting the head of a sheep. He found shortly afterwards, however, that the ca.n.a.l could be demonstrated to exist in the dog, though it was not so large a structure. Blasius seems to have been rather annoyed at the fact that a student, just beginning work with him, should make so important a discovery, and wished to claim the honor of it for himself. There is no doubt, however, now, notwithstanding the discussion over the priority of the discovery which took place at the time, that Stensen was the first to make this important observation.

Not long before, Wharton, an English observer, had demonstrated the existence of a ca.n.a.l leading from the submaxillary gland into the mouth. This might have been expected to lead to the discovery of other glandular ducts, but so far had not. As a matter of fact, the function of the parotid gland was not well understood at this time. During the discussion as to priority of discovery, Steno pointed out one fact which he very properly considers as the most conclusive proof that Blasius did not discover the duct of the gland. He says: "Blasius shows plainly in his treatise 'De Medicina Generali' that he has never sought for the duct, for he does not a.s.sign {144} to it either the proper point of beginning or ending, and a.s.signs to the parotid gland itself so unworthy a function as that of furnis.h.i.+ng warmth to the ear, so that if I were not perfectly sure of having once shown him the duct myself, I should be tempted to say that he had never seen it."

Bartholini settled the controversy, and at the same time removed any discouragement that might have arisen in his young pupil's mind, by writing to him:--

Your a.s.siduity in investigating the secrets of the human body, as well as your fortunate discoveries, are highly praised by the learned of your country. The fatherland congratulates itself upon such a citizen, I upon such a pupil, through whose efforts anatomy makes daily progress, and our lympathic vessels are traced out more and more. You divide honors with Wharton, since you have added to his internal duct an external one, and have thereby discovered the sources of the saliva concerning which many have hitherto dreamed much, but which no one has (permit the expression) pointed out with the finger. Continue, my Steno, to follow the path to immortal glory which true anatomy holds out to you.

Under the stimulus of such encouragement, it is no wonder that Stensen continued his original work with eminent success. He published an extensive article on the glands of the eye and the vessels of the nose.

Bartholini wrote to him again: "Your fame is growing from day to day, for your pen and your sharp eye know no rest." Later he wrote {145} again: "You may count upon the favor of the king as well as upon the applause of the learned." After three years at the University of Amsterdam, Steno returned to Copenhagen, where he published his "Anatomical Observations Concerning the Muscles and Glands." It was in this book that he announced his persuasion that the heart was a muscle. As he said himself, "the heart has been considered the seat of natural warmth, the throne of the soul; but if you examine it more closely, it turns out to be nothing but a muscle. The men of the past would not have been so grossly mistaken with regard to it, had they not preferred their imaginary theories to the results of the simple observation of nature." It is easy to understand that this observation created a very great sensation. It had much to do with overthrowing certain theoretic systems of medicine, and nearly a century later the distinguished physiologist, Haller, did not hesitate to proclaim the volume in which it occurs, as a "golden book."

Stensen's studies in anatomy stamp him as an original genius of a high order, and this is all the more remarkable because his career occurs just in those years when there were distinguished discoverers in anatomy in every country in Europe. When Stensen began his work in anatomy, Harvey was still alive. The elder Bartholini, the first who ever established an anatomical museum, was another of his contemporaries. Among the names of distinguished anatomists {146} with whom Stensen was brought intimately in contact during the course of his studies in Holland, France and Italy are those of Swammerdam, Van Horne, and Malpighi. There is no doubt that his intercourse with such men sharpened his own intellectual activity, and increased his enthusiasm for original investigation in contradistinction to the mere acc.u.mulation of information.

His contemporaries, indeed, exhausted most of the adjectives of the Latin language in trying to express their appreciation of his acuity of observation. He was spoken of as _oculatissimus_--that is, as being all eyes, _subtilissimus, acutissimus, sagacissimus_ in his knowledge of the human body, and as the most perspicacious anatomist of the time. Leibnitz and Haller were in accord in considering him one of the greatest of anatomists. In later years this admiration for Stensen's genius has not been less enthusiastically expressed. Haeser, in his "History of Medicine," the third edition of which appeared at Jena in 1879, says: "Among the greatest anatomists of the seventeenth century belongs Nicholas Steno, the most distinguished pupil of Thomas Bartholini. Steno was rightly considered in his own time as one of the greatest of anatomical discoverers. There is scarcely any part of the human body the knowledge of which was not rendered more complete by his investigations."

The most valuable discovery made by Stensen was undoubtedly that the heart is a muscle. It {147} must not be forgotten that in his time, Harvey's discovery of the circulation of the blood was not yet generally accepted; indeed, there were many who considered the theory (as they called it) of the English investigator as one of the pa.s.sing fads of medicine. Two significant discoveries, made after Harvey, served, however, to establish the theory of the circulation of the blood on a firm basis and to make it a definite medical doctrine. The most important of these was Malpighi's discovery that the capillaries--that is, the minute vessels at the end of the arterial tree on the surface of the body and in various organs--served as the direct connexion between the veins and the arteries. This demonstrated just how the blood pa.s.sed from the arterial to the venous system.

Scarcely less important, however, for the confirmation of Harvey's teaching was Stensen's demonstration of the muscular character of the tissue of the heart.

Some of his observations upon muscles are extremely interesting, and, though he made many mistakes in explaining their function, he added not a little to the anatomical and physiological knowledge of the time in their regard. He seems to have been one of the first to recognize the fact that in the higher animals the heart may continue to beat for a considerable time after the animal is apparently dead; and, indeed, that by irritation of the removed heart, voluntary contractions may be brought about which will continue spontaneously for some moments.

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With regard to the objections made by some, that such studies as these upon muscles could scarcely be expected to produce any direct result for the treatment of disease, or in the ordinary practice of medicine, Stensen said in reply that it is only on the basis of the anatomical, physiological, and pathological observation that progress in medicine is to be looked for. In spite, then, of the discouragement of the many, who look always for immediate practical results, Stensen continued his investigation, and even proposed to make an extended study of the mechanism of the muscular action.

In the meantime, however, there had gradually been coming into his life another element which was to prove more absorbing than even his zeal for scientific discovery. It is this which const.i.tutes the essential index of the man's character and has been sadly misunderstood by many of his biographers.

Sir Michael Foster, of Cambridge, England, in his "Lectures on the History of Physiology," originally delivered as the Lane Lectures at Cooper Medical College, San Francisco, said:--

While thus engaged, still working at physiology, Stensen turned his versatile mind to other problems, as well as to those of comparative anatomy, and especially to those of the infant, indeed hardly as yet born, science of geology. His work "De solido intra solidum" is thought by geologists to be a brilliant effort toward the beginning of their science

In 1672 he returned for a while to his native city of {149} Copenhagen, but within two years he was back again at Florence; and then there came to him, while as yet a young man of some thirty-six summers, a sudden and profound change in his life.

In his early days he had heard much, too much perhaps, of the doctrines of Luther. Probably he had been repelled by the austere devotion which ruled the paternal roof. And, as his answer to Bossuet shows, his university life and studies, his intercourse with the active intellects of many lands, and his pa.s.sion for inquiry into natural knowledge, had freed him from pa.s.sive obedience to dogma. He doubtless, as did many others of his time, looked upon himself as one of the enlightened, as one raised above the barren theological questions which were moving the minds of lesser men

Yet it was out of this sceptical state of mind, that life in Italy and intimate contact with ecclesiastics and religious, so often said to be likely not to have any such effect, brought this acute scientific mind into the Catholic Church. Nor did he become merely a formal adherent, but an ardent believer, and then an enthusiastic proselytizer. One American writer of a history of medicine, in his utter failure to comprehend or sympathize with the change that came over Stensen, speaks of him as having become at the end of his life a mere "peripatetic converter of heretics." This phase of Stensen's life has, however, as ample significance as any that preceded it.

Steno's expectations of the professors.h.i.+p of anatomy at Copenhagen were disappointed, but the appointment went to Jacobson, whose work indeed is scarcely less distinguished than that of {150} his unsuccessful rival. The next few years Stensen pa.s.sed in Paris, where he was a.s.siduous in making dissections, and where he attracted much attention; and then, somewhat later, in Italy; in 1665 and 1666 he was in Rome. Thence he went to Florence, in order to perfect himself in Italian. The next few years he spent in this city, having received the appointment of body physician to the Grand Duke, as well as an appointment of visiting physician, as we would call it now, to the Hospital of Santa Maria Nuova.

It was while at Florence that the whole current of Stensen's life was changed by his conversion to Catholicity. His position as physician to the Hospital of Santa Maria Nuova brought him frequently into the apothecary shop attached to the hospital. As a result he came to know very well the religious in charge of the department, Sister Maria Flavia, the daughter of a well-known Tuscan family. At this time she had been for some thirty-five years a nun. Before long she learned that the distinguished young physician, at this time scarcely thirty years of age, who was such a pleasant gentleman in all his ways, was a Lutheran. She began, as she told afterwards, first by prayer, and then by friendly suggestions, to attempt to win him to the Catholic Church.

Stensen, who seems already to have been well-disposed toward the Church, and who had always been known for a wonderful purity of heart and simplicity of character, listened very willingly to the naive words of the {151} old religious, who might very well have been his mother.

Many years later, by the command of her confessor, the good Sister related the detailed story of his conversion. She began very simply by telling him one day that if he did not accept the true Catholic faith, he would surely go to h.e.l.l. He listened to this without any impatience, and she said it a number of other times, half jokingly perhaps, but much more than half in earnest. As he listened so kindly, she said to him one day that he must pray every day to G.o.d to let him know the truth. This he promised to do and, as she found out from his servant (what is it these nuns do not find out?) he did pray every evening. One day, while he was in the apothecary shop, the Angelus bell rang, and she asked him to say the Angelus. He was perfectly willing to say the first part of the Hail Mary, but he did not want to say the second part, as he did not believe in the invocation of the Blessed Virgin and the saints. Then she asked him to visit the Church of the Blessed Virgin, the Santissima Nunziata, which he did. After this she suggested to him that he should abstain from meat on Fridays and Sat.u.r.days, which he promised to do, and which the good nun found out once more from his servant, he actually did do. And then the religious thought it was time to suggest that he should consult a clergyman, and his conversion was not long delayed.

Young Stensen seems to have been the object {152} of solicitude on the part of a number of the good, elderly women with whom he was brought in contact. He discussed with Signora Arnolfini the great difficulty he had in believing the mystery of the Eucharist. Another good woman, the Signora Lavinia Felice, seeing how interested he was in things Catholic, succeeded in bringing him to the notice of a prominent Jesuit in Florence. As his friend, Sister Maria Flavia, had recommended the same Father to him, he followed the advice all the more readily, and it was not long before his last doubts were solved.

It was after his conversion that Stensen received his invitation to become the professor of anatomy at the University of Copenhagen. Much as he had become attached to Florence, the thought of returning to his native city was sweet; and then besides he hoped that he might be able to influence his countrymen in their views toward the Catholic Church.

It was not long, however, before the bigotry of his compatriots made life so unpleasant for him in Copenhagen that he resigned his position and returned to Italy. Various official posts in Florence were open for him, but now he had resolved to devote himself to the service of the Church, and so he became a priest. His contemporary, the Cardinal Archbishop of Florence, said with regard to him: "Already as a member of a Protestant sect he had lived a life of innocence and had practised all the moral virtues. After his conversion he had marked out for himself so severe a method of life and had {153} remained so true to it that in a very short time he reached a high degree of perfection." The Archbishop does not hesitate to say that he had become a man of constant union with G.o.d and entirely dead to himself.

There was very little hesitation, then, in accepting him as a candidate for the priesthood, and as his knowledge of theology was very thorough, most of the delay in raising him to that dignity came from his own humility and his desire to prepare himself properly for the privilege. He made the exercises of St. Ignatius as part of his preparation, and after his ordination it was a source of remark with how much devotion he said his first and all succeeding Ma.s.ses. It was not long before the piety of Stensen's life attracted great attention.

At this time he was in frequent communication with such men as Spinoza and Leibnitz, the distinguished philosophers. It is curious to think of the ardent mystic, the pantheistic philosopher, and the speculative scientist, so different in character, having many interests in common.

It was during these years in Italy that Stensen did what must be considered, undoubtedly, his most important work, even more important, if possible, than his anatomical discoveries. This was his foundation of the science of geology. As has been well said in a prominent text-book of geology, his book on this subject sets him in that group of men who as prophets of science often run far ahead of their times to point out the path which later centuries will follow in the road of {154} knowledge. It is rather surprising to find that the seventeenth century must enjoy the privilege of being considered the cradle of geological knowledge. There is no doubt, however, that the great principles of the science were laid down in Stensen's little book, which he intended only to be an introduction to a more extensive work, but the latter was unfortunately never completed, nor, indeed, so far as we are able to decide now, ever seriously begun.

One of the basic principles of the science of geology Stensen taught as follows: "If a given body of definite form, produced according to the laws of nature, be carefully examined, it will show in itself the place and manner of its origin." This principle he showed would apply so comprehensively that the existence of many things, hitherto apparently inexplicable, became rather easy of solution. It must not be forgotten that before this time two explanations for the existence of peculiar bodies, or of ordinary bodies, in peculiar places, had been offered. According to one school of thought, the fossils found deep in the earth, or sometimes in the midst of rocks, had been created there. It was as if the creative force had run beyond the ordinary bounds of nature and had produced certain things, ordinarily a.s.sociated with life, even in the midst of dead matter. The other explanation suggested was that the flood had in its work of destruction upon earth caused many anomalous displacements of living things, and had buried some of the {155} animals under such circ.u.mstances that later they were found even beneath rocks, or deep down in the earth, far beyond where the animals could be supposed to have penetrated by any ordinary means during life.

Stensen had observed very faithfully the various strata that are to be found wherever special appearances of the earth's surface were exposed, or wherever deep excavations were made. His explanation of how these various strata are formed will serve to show, perhaps better than anything else, how far advanced he was in his realization of ideas that are supposed to belong only to modern geology. He said: "The powdery layers of the earth's surface must necessarily at some time have been held in suspension in water, from which they were precipitated by their own weight. The movement of the fluid scattered the precipitate here and there and gave to it a level surface."

"Bodies of considerable circ.u.mference," Stensen continues, "which are found in the various layers of the earth, followed the laws of gravity as regards their position and their relations to one another. The powdery material of the earth's strata took on so completely the form of the bodies which it surrounded that even the smallest apertures became filled up and the powdery layer fitted accurately to the surface of the object and even took something of its polish."

With regard to the composition of the various strata of the earth, the father of geology {156} considered that if in a layer of rock all the portions are of the same kind there is no reason to deny that such a layer came into existence at the time of creation, when the whole surface of the earth was covered with fluid. If, however, in any one stratum portions of another stratum are found, or if the remains of plants or animals occur, there is no doubt that such a stratum had not its origin at the time of creation, but came into existence later.

If there is to be found in a stratum traces of sea salt, or the remains of sea animals, or portions of vessels, or such like objects, which are only to be encountered at the bottom of the sea, then it must be considered that this portion of the earth's surface once was below the sea level, though it may happen that this occurred only by the accident of a flood of some kind. The great distance from the sea, or other body of water, at the present time, may be due to the sinking of the water level in the neighborhood, or by the rising up of a mountain from some internal terrestrial cause in the interval of time.

He continues:--

If one finds in any layer remains of branches of trees, or herbs, then it is only right to conclude that these objects were brought together because of flood or of some such condition in the place where they are now found. If in a layer coal and ashes and burnt clay or other scorched bodies are found, then it seems sure that some place in the neighborhood of a watercourse a fire took place, and this is all the more sure when the whole layer consists of ashes and {157} coal. Whenever in the same place the material of which all the layers is composed is the same, there seems to be no doubt that the fluid to which the stratum owes its origin did not at different times obtain different material for its building purposes.

In respect to the mountains and their formation, Stensen said very definitely:--

All the mountains which we see now have not existed from the beginning of things. Mountains do not, however, grow as do plants.

The stones of which mountains are composed have only a certain a.n.a.logy with the bones of animals, but have no similarity in structure or in origin, nor have they the same function and purpose.

Mountain ranges, or chains of mountains as some prefer to call them, do not always run in certain directions, though this has sometimes been claimed. Such claims correspond neither to reason nor to observation. Mountains may be very much disturbed in the course of years. Mountain peaks rise and fall somewhat. Chasms open and shut here and there in them, and though there are those who pretend that it is only the credulous who will accept the stories of such happenings, there is no doubt that they have been established on trustworthy evidence.

In the course of his observations in Italy, Stensen had seen many mussel sh.e.l.ls, which had been gathered from various layers of the earth's surface. With regard to the sh.e.l.ls themselves, he said that there could be no doubt that they had come as the excretion of the mantle of the mussel, and that the differences that could be noted in them were in accordance with the varying forms of these animals. He pointed out, however, that some of the mussel sh.e.l.ls found in {158} strata of rock were really mussel sh.e.l.ls in every respect as regards the material of which they were composed as well as their interior structure and their external form, so that there could be no possible question of their origin. On the other hand, a certain number of the so-called mussel sh.e.l.ls were not composed of the ordinary materials of which such sh.e.l.ls are usually made up; but had indeed only the external form of genuine sh.e.l.ls. Stensen considered, however, that even these must be regarded as originating in real mussel sh.e.l.ls, the original substance having been later on replaced by other material. He explained this replacement process in very much the same way that we now suggest the explanation of various processes of petrification.

There is no doubt that in this he went far beyond his contemporaries, and pointed out very clearly what was to be the teaching of generations long after his own.

The same principles he applied to mussel sh.e.l.ls, Stensen considered must have their application also to all other portions of animal bodies, teeth, bones, whole skeletons, and even more perishable animal materials that might be found buried in the earth's strata. His treatment of the question of the remains of plants was quite as satisfactory as that of the animals. He distinguished between the impressions of plants, the petrification of plants, the carbonization of plants, and then dwelt somewhat on the tendency of certain minerals to form dendrites, that is, branching {159} processes which look not unlike plants. He pointed out how easy it is to be deceived by these appearances, and stated very clearly the distinction between real plants and such simulated ones.