Leonardo da Vinci - the anatomist (1930) 8
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McMurrich JP. Leonardo da Vinci - the anatomist. (1930) Carnegie institution of Washington, Williams & Wilkins Company, Baltimore.
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Leonardo da Vinci - The Anatomist
Chapter VIII General Anatomy and Physiology
In Leonardo’s time a cleavage between anatomy and physiology, between the study of structure and function, did not exist. As an artist he was interested in form and as a student of mechanics he was interested in function, but the two could not be separated; there was no question as to whether form determined function or function determined form; each organ was believed to be designed and created for a special purpose and to be perfectly adapted to perform that purpose. The extreme teleology of Aristotle and Galen had been accepted with satisfaction by the Arabs, and the mediaevalists received it without question because it was in harmony with the teachings of the Church; and so, for Leonardo, the teleological view of Nature was the only one available. “The Author” he says “does not make anything superfluous or defective” (QII, 3), and again “Nothing is superfluous and nothing lacking in any kind of animal and product of Nature” (QI, 4v), to which dictum he adds the qualifying phrase “unless the defect comes from the manner in which it acts,” apparently referring to the abnormal action of a pathological organ rather than to a defect in a normal one. “The anivia can never be affected by the corruption of the body, but acts in the body like the wind which produces the sound of the organ, in which, if one of the pipes is injured, the wind can not produce a good result in the pipe” (Tr. 71). The same idea of perfection in form and function is seen in the statement that “Nature is said always to produce its effects in the easiest way and in the shortest time possible” (QI, 4).
With such beliefs, the dissociation of form and function was hardly possible. It did not take place until much later and may be traced back to the formulation of Cuvier’s theory of types. For while Cuvier fully recognized the interdependence of structure and function and made it the basis of his investigations, his theory of types led to the development by Serres and Geoffroy St. Hilaire of the doctrine of unity of plan, according to which “Nature tends to repeat the same organs in the same number and in the same relations, and varies to infinity only their form.” And so morphology became divorced from physiology, probably to the detriment of both, by becoming a search for homologous parts throughout the animal kingdom — form, structure and relations being the only criteria for homology, since function was dependent upon form.
But all this developed three centuries after Leonardo’s time; he, like his contemporaries, followed the teaching of Galen, and not only in this particular, but also in his general conception of the phenomena of life. The naive monistic materialism of the early Greek philosophers soon gave place to a dualism that has persisted even until today, a recognition of force or energy as something apart from matter, though acting on it. A lump of clay was mere matter, a living body was matter energized by a vital force, the pneuma, an imponderable, unsubstantial something, derived from the air in respiration and elaborated by the heart, whence it was distributed throughout the body. Some such concept was inevitable. How else could the characteristic phenomena exhibited by living organisms be explained, how else the difference between living and dead bodies, in the days when chemistry did not exist? As Sir Clifford Allbutt has pointed out, the pneuma of the ancients was their substitute for oxygen; it played in the animal economy essentially the same role as that element, though, since it was a mere concept and not a demonstrable entity, its mode of action necessarily remained obscure. It was the vital spirit, disturbance of which produced disease and failure of which was death. Its recognition goes back at least as far as Hippocrates and, as has been said, it is with us today, even though oxygen may have robbed it of some of its powers and properties.
Leonardo does not use the word pneuma; it disappeared from use with the disappearance of the Greek language in western Europe. Instead he uses such terms as vento, spiritus and anima, the last having sometimes a special significance, corresponding to the psychic pneuma of Galen, mediating consciousness and the idea of individuality, though hardly with the theological attributes usually attached to the word soul. Thus in AnB, 2 there is a passage headed ‘‘How the five senses are officials of the soul (anima)” in which one finds the following:
“The seat of the soul is in the judicial part (of the brain) and this seems to be in the place where all the senses come together and which is termed the sensorium commune ( senso commune). It is not everywhere in the body as some have thought, but all in this part; for if in all parts it would not be necessary for the instruments of sense to make a concourse in a single place.” . . . “As the sensorium gives to the soul and not the soul to the sensorium, when the sensorium, the official of the soul, is wanting there is wanting to the soul in such a life the knowledge of the office of the sense, as is seen in mutes and in those born blind.”
Nor do vento and spirito always have the meaning of pneuma; vento is also employed in the more usual sense of wind and spiriti may denote the “spirits of the vasty deep,” with which the necromantists claimed to have dealings but of whose existence Leonardo had serious doubts (AnB, 28v, 31v and 31).
What Leonardo’s concept of the pneuma or anima may have been, whether he regarded it as peculiar to living organisms or as identical with the forces acting on non-living objects, is of interest. To the Ancients it was undoubtedly a peculiar vital force, derived from the air drawn into the lungs and elaborated by the innate heat implanted in the left side of the heart. Galen recognized three varieties of pneuma, the psychic, elaborated in the rete mirabile of the brain; the spiritual, distributed from the left side of the heart by the arteries; and the animal, distributed by the veins and having its origin in the liver, and, in accordance with this idea the mediaeval anatomists, such as Mondino, named the contents of the three ventres of the body respectively the membra animata, spiritualia and naturalia. To this arrangement and to the principal involved in it Leonardo apparently subscribed, for in a sketch showing the general arrangement of the organs (QIV, 3) the thorax is labeled as the receptacle for the spiritual organs and the abdomen as that for the material organs, and in other drawings (QIII, 3v; QV, 1 and 20v) he indicates the diaphragm as the separation between the spiritual and the material parts.
But there are indications that Leonardo did not accept the classical tradition in all its details. He was so far advanced toward the modern scientific viewpoint as to refer, when possible, explanations of phenomena to the action of known physical forces, rather than to seek them in hypothetical, unknown agencies. He enunciates his credo in this respect in the following words:
“Weight, pressure and accidental movement, together with resistance, are the four accidental powers in which all the visible works of mortals have their existence and their end.” (SK, II, 116v.)
In accordance with that belief he dismisses the idea of innate heat, so greatly stressed by the ancients, and assigns the warmth of the heart to the —
“rapid and continuous motion of the blood producing friction on the cellular walls of the upper ventricle, as well as by its general motion. Thus the blood is heated and subtilized so that it can penetrate the pores and give life and spiritus to the members.” (QI, 4.)
That he regarded the pneuma as merely a special manifestation of one or more of the physical forces mentioned in the passage quoted above (SK, II, 116v) is not so clear, but it may be noted that his definition of force applies equally to the concept of the pneuma. This definition is as follows:
“Force I define as a spiritual power, incorporeal and invisible, which, with brief life is produced in those bodies, which, as the result of accidental violence, are brought out of their natural state and condition.” (B, 63; cf. A, 34v.)
It may be, however, that he regarded the pneuma as one of the forms of “accidental violence” that produced force.
As regards the constitution of matter he accepted as fundamental the four elements of Empedocles: fire, earth, air and water.
“Man was termed by the ancients a microcosm ( mondo rninore ) and assuredly the epithet is well taken. In effect man is composed of earth, water, air and fire; the body of the earth is the same.” (A, 55v.)
He also accepted the Empedoclean theory of two forces, love and discord, attraction and repulsion, acting on these elements —
“since one sees water expelling the air and fire that have entered from the heat in the bottom of the cauldron and escape by the bubbles at the surface of the boiling water. Also the flame attracts the air and the heat of the sun draws up the water in the form of a moist vapor, which then falls again as inspissated and heavy rain.” (QI, 1.)
It is strange that Leonardo nowhere suggests the possibility of these elements being composed of lesser particles, the atoms imagined by Democritus, accepted by Plato and made popular by Epicurus and Lucretius. He knew of Epicurus, quoting with disapproval his idea that the sun was no larger than it seemed to be (F. 5), but of Lucretius he makes no mention, although the De rerum natura was first printed in Brescia in 1473, and again in Verona in 1486. He did, however, know of the “elements” recognized by the alchemists, inflammable sulphur, volatile quicksilver and incombustible and stable salt, but his disapproval of the alchemists and all their works (AnB, 31v) led to a rejection of their theories. Thus he says (CA, 76v) :
“The lying interpreters of nature assert that quicksilver is a constituent common to all metals; they forget that nature varies its constituents according to the variety of the things it desires to produce in the world.”
The concluding sentence of this statement might be taken to indicate recognition of a multitude of elements, but it may merely refer to varying admixtures of the four classical elements.
Leonardo’s outlook was so sane, so scientific, that it is almost a relief to find in his note-books some traces of the mysticism so prevalent in his day. One such trace is to be found in his acquiescence in the idea that man is a microcosm, similar in all essential members to the macrocosm. The idea is an old one, tracing back in its fuller development to the Neo-platonists of the third and fourth centuries, who taught that man was composed of the same elements as the rest of the cosmos and was endowed with a portion of the world-soul which pervaded all things; materially and spiritually he was therefore a miniature cosmos, subject through his moiety of the world-soul to all the influences affecting the greater cosmos. The inherent mysticism of the idea appealed to the Arabian commentators, and during the Middle Ages was made familiar by the writings of Hildegarde of Bingen and later by the teachings of Grosseteste and Albertus Magnus, the Doctor Universalis. It gave a foundation for the belief of astrologers in the influence of the stars in their courses on the lives of man, a belief that lingered, nay flourished, long after Leonardo’s time.
He, however, was not interested in the astrological bearings of the idea, it was the structural analogies of the parts of the human body and those of the earth that appealed to him. The opening sentence of a passage in which he declares his belief in the microcosm idea has already been quoted (p. 96); in the continuation of that passage (A, 55 v) he compares the bones which are the framework and support of the flesh to the rocks which are supports for the soil; the respiratory movements of the lungs are likened to the ebb and flow of the tides, which are the breathing of the world; the veins, arising in a pool of blood (the heart), spread their branches throughout the body, just as the ocean fills the body of the Earth with infinite veins of water. Only tendons ( nervi ) are lacking in the Earth, since tendons produce movement and the Earth is stable without movement; “but in all other things man and the Earth show a great similarity.” In the Leicester Codex (fol. 34) he gives a somewhat more detailed comparison that it is worth while to transcribe.
“Consequently it may be said that the Earth has a vegetative soul and that its bones are the series of conglomerations of rocks which make the mountains; its cartilages are the tufas; its blood are the veins of water; the lake of blood contained within the heart is the ocean; its breathing is the increase and diminution of the blood through the pulse and so, in the Earth it is the ebb and flow of the sea; and the heat of the world-soul is fire that is infused throughout the Earth and the seats of the vegetative soul are the fires, which, in different places of the Earth breathe in hot springs, in sulphur mines and in volcanos, as at Mongibello in Sicily and at several other places.”
These are passages in which the idea is stated most completely, but there are allusions to it in others. Thus in QI, 2 he speaks of fifteen figures illustrating the cosmography of the “minor mondo” in the same order as was employed by Ptolemy in his Cosmography, and in CA, 171, he again draws comparison between the veins and the rivers and streams of the Earth, pointing out, however, in still another passage a difference, in that —
“The origin of the sea is the reverse of that of the blood, for the sea receives into itself all the rivers, which are totally produced from the aqueous vapors that have ascended into the air, while the sea of blood is the source of all the veins.” (AnA, 4.)
It is noteworthy that in none of these passages is there any suggestion of astrological implications; they are merely expressions of fanciful structural analogies.
With the doctrine of the four elements, that of the four humors with their definite qualities was so closely linked that it is a natural inference that Leonardo gave it credence also. And yet one finds but little reference to it in the note-books; he mentions the humors collectively only, not individually.
“The cause that in all the kinds of animate bodies moves the humors against the natural tendency of their weight is undoubtedly that which moves the water contained within the terrestrial veins.” (CA, 171.)
Of course he knew of the blood, phlegm and yellow bile, and there is indirect evidence that he also accepted the existence of the more elusive black bile, since in more than one drawing he represents a direct communication between the liver and the spleen (e.g. Q III, lOv) (fig. 52), apparently based on the Galenic theory that the black bile, elaborated in the liver, passed to the spleen and thence to the stomach.
The chief interest that lay in the doctrine of humors was the part it played in the etiology of disease. In the normal bod} r they were in a proper balance, but if from any cause any one of them should be produced in too great abundance or in a lessened quantity disease resulted. It was a plausible and consistent theory, and since the qualities of the humors, hot, cold, moist and dry, were known, the therapeutic methods that should be employed were indicated. Leonardo, however, when he writes of the cause of disease does not refer it to a dyscrasia of the humors, but of the elements.
“It is necessary to understand what sort of thing is man and what life is, what health is and how an equality, a concordance of the elements maintains it and how discordance of them threatens and undoes it” (CA, 270). . . “Medicine is the readjustment of elements that have become disequalized; disease is the discordance of elements that are united in the living body.” (Tr. 4.)
The practical difference is slight, for the qualities of the humors were also those of the elements. However, the etiological significance of the humors was a matter pertaining to medicine and Leonardo’s anatomical studies were pursued for the benefit of art and science, rather than for practical medicine. Indeed like Montaigne a few years later, he had but a poor opinion of the methods and practise of physicians.
"Endeavor to preserve your health,” he said, "and this you will succeed in doing so much the more, the more you keep away from doctors. For their mixtures arc kinds of alchemy, the books on which are not less numerous than those that exist on medicine.” (AnA, 2.)
And still more harshly he comments:
“Every man desires to gain wealth that he may give it to the doctors, the destroyers of life; therefore they ought to be rich.” (F, 96.)
After Aristotle’s time it was customary in anatomical treatises, after referring to the elements and the humors, to describe the body as composed of similar and dissimilar parts, the former corresponding approximately to what are now termed tissues, the latter to organs or members. If a lump of fat were divided into two parts, each resembled the other and was still fat, whereas if a foot or hand were divided, the two parts did not resemble each other. Hence the terms similar and dissimilar. The similar parts were structural units of a higher grade than the elements or humors; as Avicenna puts it, the members (i.e. similar parts) were formed by commixtion of the humors, the humors by commixtion of foods and foods by the commixtion of the elements.
Aristotle and Galen mention a number of these similar parts but differ somewhat in their enumeration, for while Aristotle includes such substances as milk and semen, which Galen omits, the latter adds the crystalline and vitreous humors of the eye and also the proper substance of such organs as the stomach, intestines and uterus. Avicenna materially reduces the number, omitting such obvious items as fat, skin and nails, mentioning only bone, cartilage, nerve, tendon (chorda), ligament, arteries, veins, membrane (panniculus) and flesh ( caro ). The distinction of tendons and ligaments is not very clear and he apparently recognizes two kinds of flesh, that forming the substance of muscle and that filling spaces not occupied by other material, meaning thereby glandular tissue, such as that of the thyroid and pancreas.
Leonardo does not discuss the similar parts as such, but in his account of the structure of muscles (QII, 18v) he mentions certain of them in a manner distinctly reminiscent of Avicenna; certainly in this case his source was Avicenna rather than Mondino, since the latter author while mentioning the existence of similar parts, purposely omits an enumeration of them, since they could not be demonstrated in an Anatomy. The similares mentioned by Leonardo are bone, cartilage, nerve, veins, arteries, these incidentally, and tendons (corde), ligaments, membranes ( panniculi ), flesh, pellicles and fat, but when one attempts to gain a clear idea of what these terms denoted difficulties are encountered. Leonardo was approximately one hundred and fifty years before Leeuwenhoek and Malpighi and the application of the microscope to anatomy, and had therefore to rely mainly on form, color and consistence for the distinction of the various tissues and, further, his notes were recorded at odd times over a long period of years, allowing of uncertainty in the use of the terms employed.
Notwithstanding Galen’s attempt to correct Aristotle’s confusion of nerve and tendon it reappears in Avicenna and is even more marked in Leonardo’s notes, in which tendons are usually indicated by corde, but sometimes by nervi, and, conversely, nerves are sometimes termed corcle. Thus on AnB, 2, he says —
“The nervi with their muscles serve the corde as do the soldiers their leaders ( condollieri ); the corde serve the senso commune as the leaders do the captains; and the senso commune serves the anima as the captains do their lord.”
The point of this is lost unless one translates nervi as tendons and corde as nerves.
The definition of the term panniculi (membranes), “joined to the flesh and interposed between the flesh and the tendon (nervi)] usually they are joined to the cartilage” (Q II, lSv), is not clear, but in other passages (An A, IIv, 18) it is evident that it denotes the periosteum or (AnA, 18) the capsular ligaments of the joints. It would seem, then, that it denoted any connective tissue membrane and might include three varieties, tendinous, nervous and composite, the latter consisting of tendon, nerve, muscle, vein and artery. But here, again, Leonardo’s definitions do not clearly define; perhaps a tendinous panniculo was one in which the fibers were clearly arranged in bundles, and a nervous one in which they were not. The composite variety seems to indicate the platysma, but the term pellicle apparently denotes the same combination of parts. Furthermore, while the articular capsules are sometimes described as membranes, they are also termed ligaments (.AnA, 15v), the aponeuroses of the abdominal muscles are termed cartilage (AnB, 15), and cartilage itself is said to be “indurated tendon or hardened bone” ( Q 1 1 , lSv). It would seem that Leonardo had an inkling of the fundamental relationships of all the varieties of connective tissue and was groping for a method of expressing them.
The opening chapter of Avicenna’s Summa on the muscles reads as follows:
“God in his wisdom therefore controlled it by giving it strength ( grossitiem ) which he produced by a commingling of fibers (villi) in a substance composed of these and of ligaments, and the meshes of these he filled with flesh (caro) and this itself he covered by a membrane (panniculus), and in the middle he placed a perpendicular like a tendon (chorda) of the substance of nerve. And from this, when all was done, there is a member composed of nerve and ligament and the fibers of these, of the filling flesh and the covering membrane. And this member itself is a muscle.”
Leonardo’s conception of flesh was undoubtedly the same as Avicenna’s, but his statement of it is obscured by an interchange of the words “muscle” and “flesh.” He says, “Flesh is composed of muscle, corda, nerve, blood (i.e. veins) and artery” (Q II, 18v), and if “muscle” be substituted for “flesh” and “flesh” for “muscle” the agreement with Avicenna is complete.
Fat is mentioned as a substance occurring beneath the skin and filling up the depressions between the muscles. It is said to be of a spongy or viscous consistency and to contain little vesicles full of air, which condense or rarefy according to the increase or rarefaction of the muscle substance (G, 26).
So much for Leonardo’s ideas concerning the basic structural constitutents of the body. They were essentially those of Galen as transmitted by Avicenna, but showing here and there indications of independence, originality and imagination. The dissimilar parts or organs, formed by the conjunction of various similares, will be considered in succeeding chapters, but the general question as to their arrangement in the body may be considered here. The extreme teleology of the mediaeval anatomists demanded a purpose in all things. That the animal, spiritual and natural parts should be located respectively in the head, thorax and abdomen seemed quite reasonable, but why, Leonardo asks “is man divided by the brain, rectum, the fork (of the legs), lips, nose, penis and anus and lung, but not by the stomach and bladder (gall-bladder)” (QI, 13), that is to say, why should the stomach and gall-bladder be placed asymmetrically in the body, while the other organs named are symmetrical? The answer to the question is partly to be found on QII, 15, in a passage headed “The balancing of the weight of the right and left side,” in which it is held that the heart is inclined to the left in order that it and the spleen may together balance the liver on the right, the stomach on the left is balanced by the caecum, the duodenum on the right balances the ileum on the left, while the jejunum and rectum are placed in the middle line. 1 The explanation seems somewhat lacking today, even with our imperfect knowledge of developmental mechanics, but it was no doubt acceptable in the early part of the sixteenth century.
Leonardo’s general physiology was even more purely Galenic than his anatomy. Wastage of the body substance was continually going on. Food underwent a concoction in the stomach whereby it was converted into chyle, which was carried to the liver and there was subjected to a second concoction. This converted it into blood, with the separation of certain impurities, yellow and black bile, and the excess of water, this last passing to the kidneys. From the liver the blood passes to the heart, whence it is distributed to the various parts of the body for their restoration, a portion of it, however, being subtilized into pneuma ( anima ) by the heat developed by the pulsation of the heart. This passed through minute pores in the septum of the ventricles and was distributed to the body by the arteries. The lungs served to moderate the heat of the heart. Quite a plausible and consistent theory when one makes allowance for ignorance of the circulation of the blood and of the chemical processes involved in metabolism.
1 In this passage Leonardo becomes confused in his use of the terms “right” and “left,” placing the caecum and duodenum on the left. Correction has been made above.
The philosophic side of Leonardo’s mind found interest in the idea of the continual destruction and repair, death and rebirth of the tissues of the body, and he comments upon it at some length in a passage (Anil, 28) headed “How the body of animals continually dies and is born again.” He compares the life of the body to the flame of a candle —
“formed by the nourishment given to it by the fat of the candle, which life is thus continuously renewed by very rapid aid from beneath, in proportion as the upper part is consumed and dies, and in dying becomes changed from radiant light to dingy smoke. And this death goes on as long as the smoke continues; and the period of duration of the smoke is the same as that which feeds it, and in a moment the whole light dies and is entirely regenerated by the movement of that which nourishes it. And its life receives from it also its ebb and flow, as the flicker of its point serves to show us.”
So, he continues —
“The flesh of animals is restored by the blood, which continually is generated from their nourishment, and this flesh unmakes itself and returns by the meseraic arteries and passes to the intestines, where it putrefies by a putrid and puant death, as is shown by their expulsions and vapors; just as does the smoke and fire given for comparison.” . . . “Man and the animals are merely a passage and channel for food, a tomb for other animals, a haven for the dead, giving life by the death of others, a coffer full of corruption.” (CA.76v.)
But why, except for accident and disease, should not the restoration of the wasted tissues go on indefinitely? Why should “the old who enjoy good health die through lack of nutrition” (AnB, 10v)? Seeking an answer to this question Leonardo seizes the opportunity for making an autopsy of a centenarian, who —
“did not feel any failure in the body except weakness, and thus sitting on a bed in the hospital of Santa Maria Nuova of Florence, without any movement or sign of any accident, he passed from this life.” (AnB, lOv.)
And lie found that —
“The veins of the aged acquire great length and so become tortuous, those that arc wont to lie straight, and they become so thick in their wall that they close and prevent the movement of the blood. And from this comes death in the aged, without illness.” (AnB, 11 v. )
He figures the tortuous vessels and compares them with the straight vessels of a child (fig. 50), giving the first record of a case of arteriosclerosis and the first foundation for the aphorism that a man is as old as his arteries.
Life then is a question of nutrition.
“We support our life by the death of others. In a dead thing there remains insensible ( ?sentato ) life, which, united to the stomach of the living, takes again sensitive and intellectual life.” (H, 89.)
This statement might be justified by an appeal to the teachings of modern chemistry, but from Leonardo it is mere speculation. He was, however, groping for an explanation of life more fundamental, more satisfying than that which made it merely a question of nutrition, and in his gropings he suggests possibilities, whose full significance, far beyond the knowledge of his day, is interesting in the light of modern mechanistic theories. “Where there is life there is heat and where there is vital heat there is movement of the humors” (CA, 171), and he carries this idea back to its source in the sun by the statement that “all vital principle descends from it (i.e. the sun) since the heat there is in living creatures proceeds from this vital principle” (F, 5). But more startling, because so modern, is the assertion that “Motion is the cause of all life” (H, 141).
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Reference: McMurrich JP. Leonardo da Vinci - the anatomist. (1930) Carnegie institution of Washington, Williams & Wilkins Company, Baltimore.
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