Malpighi, Marcello

MALPIGHI, MARCELLO

(b. Crevalcore, Bologna, Italy, baptized 10 March 1628; d. Rome, Italy, 29 November 1694)

medicine, microscopic and comparative anatomy, embryology.

Malpighi was the son of Marcantonio Malpighi and Maria Cremonini. In 1646 he entered the University of Bologna, where his tutor was the Peripatetic philosopher Francesco Natali. On Natali’s advice Malpighi in 1649 began to study medicine. He first attended the school conducted by Bartolomeo Massari, then that of Andrea Mariani; with Carlo Fracassati he was among the nine students allowed to attend the dissections and vivisections that Massari conducted in his own house.

Malpighi graduated as doctor of medicine and philosophy in 1653; three years later, still in Bologna, he began teaching as a lecturer in logic, but toward the end of the year he was called to the chair of theoretical medicine at the University of Pisa. The three years that he spent in Pisa were fundamental to the formation of Malpighi’s science. Influenced by Giovanni Alfonso Borelli, who was then professor of mathematics in the same university, Malpighi turned from Peripateticism to a “free and Democritean philosophy.” He also participated in animal dissections in Borelli’s home laboratory and, through Borelli, entered the scientific orbit of the school of Galileo, which was at that time best represented in Tuscany itself, in the Accademia del Cimento (1657–1667).

By 1659, however, Malpighi was no longer able to tolerate the Pisan climate. He therefore returned to Bologna to become extraordinary lecturer in theoretical medicine. Toward the end of 1660 he assumed the ordinary lectureship at the university in practical medicine. In 1662 he went to the University of Messina, where he held the principal chair of medicine; four years later he returned to Bologna to lecture in practical medicine again. A letter of 28 December 1667 asked him to undertake scientific correspondence with the Royal Society of London; Malpighi agreed, and the society subsequently supervised the printing of all his later works. In 1691 Malpighi was called to Rome as chief physician to Pope Innocent XII. He died there, in his apartments in the Quirinal Palace.

Malpighi’s first—and fundamental—work is the De pulmonibus, two short letters which he sent to Borelli in Pisa and which were published in Bologna in 1661. After his return to Bologna in 1659 Malpighi, together with Carlo Fracassati, continued to conduct dissections and vivisections. In the Course of these he used the microscope to make fundamental discoveries about the lungs, which he quickly announced in the letters to Borelli.

According to the traditional quaternary system, the lungs were fleshy viscera, endowed with a sanguine nature and hot-humid temperament. Having subjected them to microscopical examination, Malpighi found them to be an aggregate of membranous alveoli opening into the ultimate tracheobronchial ramifications and surrounded by a capillary network. He had thus discovered the connections, until then sought in vain, between the arteries and the veins. His observations were of basic significance for two reasons—the pulmonary parenchyma (and subsequently the other parenchymas) for the first time could be seen to have a structure, and the observation of the capillaries confirmed the theory of the circulation of the blood and assured its general acceptance.

Malpighi’s mastery of microscopic technique was apparent even in De pulmonibus. He used instruments of different magnifying powers and made observations with both reflected and transmitted light. He prepared Specimens in a number of ways, including drying, boiling, insufflation (of the tracheobronchial tree or of systems of blood vessels), vascular perfusion, deaeration (by curshing), corrosion, or a combination of these methods. In choosing to examine the frog, Malpighi was able to avail himself of the so-called “microscope of nature.” He was able to visualize, with a relatively small magnification, so minute a feature as the capillary (the capillary network itself is so fine in mammals that Malpighi was never able to observe it with the microscopes available to him). Malpighi acutely remarked that nature is accustomed “to undertake its great works only after a series of attempts at lower levels, and to outline in imperfect animals the plan of perfect animals.”

Malpighi saw the structure of the lung as air cells surrounded by a network of blood vessels; he interpreted this structure as a well-devised mechanism to insure the mixing of particles of chyle with particles of blood—in other words, for the conversion of chyle to blood (then called hematosis), a function that the Galenists attributed to the liver. Jean Pecquet had shown in 1647 that the chyle, instead of being conveyed to the liver, was introduced into the blood in the superior vena cava, at a point shortly before that vessel reached the heart, and was then distributed to the lungs through the pulmonary artery.

In the four years, 1662–1666, that he spent at the University of Messina, Malpighi enthusiastically continued his researches on fundamental structures, making use also of marine animals from the Strait of Messina. He published the results of these researches in a series of treatises in 1665–1666. These were devoted mainly to three major topics—neurology, adenology, and hematology.

The short works De lingua (Bologna, 1665) and De externo tactus organo (Naples, 1665) are closely linked to each other. In De lingua,Malpighi reported peeling two layers from the surface of the tongue—the horny layer and the reticular (or mucous) layer that is now named for him—and thus exposing the papillary body, in which he distinguished three orders of papillae. He speculated that these papillae could be reached through pores in the epithelium and thereby stimulated by “sapid” particles dissolved in the saliva, the organismal liquid the significance of which had been recognized just a few years previously by Nicholas Steno. It is easy here to recognize the influence of Galileo, who in ll saggiatore (1623) had suggested that the very small taste particles, when “placed on the upper surface of the tongue and, mixed with its moisture, penetrate it and carry the tastes, pleasant or otherwise, according to the differences in the touching of the different shapes of these tiny corpuscles, and according to whether they are few or many, faster or slower.”

Malpighi’s discovery of the sensory receptors—the papillae of the tongue were followed by the cutaneous (or tactile) papillae—formed part of a wider neuroanatomical research. In the treatise De cerebro, which was published in 1665 with De lingua, he dealt mainly with the white substance of the central nervous system, which he found to be composed of the same fibers that form the nerves. Malpighi conceived of these fibers as long, fine channels filled with a liquid—the nerve fluid—which was secreted by the cortical gray matter, or, more precisely, by the cortical glands. In his later treatise De cerebri cortice (1666), Malpighi claimed to have demonstrated these glands, but his results were in fact due to an artifact.

On the basis of his observations, whether true or false, Malpighi in any event succeeded in constructing a mechanism to encompass the entire neural course from the cortex of the brain to the peripheral endings of the nerves: the neuron, in which the transmission of the nervous impulse could be equated with the transmission of a mechanical impulse through a liquid mass in accordance with Pascal’s principle.

During his years in Messina, Malpighi made further investigations into the structure of another mechanism fundamental to his iatromechanical atomism: the gland, or secretion machine. The function of this mechanism was to select specific particles of blood brought by an afferent artery, to separate them from others flowing back through an efferent vein, and to introduce them, as an independent liquid, into an excretory duct. The sieve may thus be used as a convenient model (“cribrum” and “secretio” are even etymologically the same); it offers an a priori explanation of the operation of the secreting mechanism by postulating a proportionality of form and dimension between the pores and the particles to be separated. Malpighi certainly recognized that he could not investigate this “minima simplexque meatuum structura” directly, but he did not abandon his search for the mechanism that might contain the pores. This he localized, a priori, at the point at which the smallest ramifications of the artery, vein, and duct are joined together.

Malpighi continued to search for ever finer and more minute structures within the glandular parenchyma. These investigations were stimulated by the discovery of the pancreatic duct (by Wirsüng in 1642), the testicular duct (by Highmore in 1651), the submandibular duct (by Wharton in 1656), and the parotid duct (by Steno in 1660).

The secreting mechanism devised by Malpighi was based on a follicle that, on one hand, is continuous into the secretary tubule, and, on the other, is surrounded by the ultimate ramifications of the arteries, veins, and nerves. In passing from the artery to the vein, the blood channel and the contiguous glandular follicle are permeable to the particles that must be eliminated and impermeable to the particles that must be eliminated and impermeable to the particles of venous blood. By analogy with the sieve, and without invoking vitalistic arguments, secretion can thus be explained in purely mechanical terms. In De renibus Malpighi set down a series of convincing observations in support of his system. He skillfully made use of staining techniques by affusion to show the renal tubules, both straight and twisted, while by injecting coloring into the arteries he was able to demonstrate the tufts of vessels attached to the branches of the interlobular arteries. He believed, however, that the ampullar extremities of the renal tubules (the Malpighi corpuscles) were enclosed within the vascular tufts.

Malpighi reiterated and developed his theory of glandular structure in the epistolary dissertation De structura glandularum conglobatarum consimilique partium, dated June 1688 and published in London the following year. Although the “conglobate” glands of Sylvius—that is, the lymph nodes—are emphasized in the title, less than half the treatise is devoted to them. For the rest, Malpighi reported additional observations on glands that were already known and considerably expanded his earlier work on the secretary mechanism. He also included remarks on the glandular membranes (later classified by Bichat as serous and mucous).

Having established the capillary circulation and devised a mechanism to explain hematosis; having defined and systematized a nervous mechanism endowed with highly acute sensory receptors; and having postulated a secreting mechanism, Malpighi turned to an analysis of the blood—the universal fluid necessary to all these machines. His chief hematological treatise, De polypo cordis, appeared in 1666 (or 1668?) as an appendix to De viscerum structura.

“Heart polyps” had been identified for some time and with a certain frequency, especially in patients who had died from severe cardiorespiratory insufficiency. Previous researchers had explained such polyps in various ways, even invoking traditional humoral theory. Malpighi, however, considered these lesions to be the result of an intravitam process of coagulation, which had as its model the coagulation of blood extracted from the organism. The study of coagulum was thus fundamental, and culminated in Malpighi’s demonstration that the “phlogistic crust” was, despite its whitish color, derived from the whole blood that “confuses our poor eyes with its purple [color].” To this end he broke the blood down into its component parts (a method that he had successfully employed in his studies of viscera and organs) by continuing artificially in the coagulum the separation (into coagulum and serum) that occurs naturally when blood is extracted from an organism. Malpighi found that the coagulum, after repeated washings, “from being intensely red and black becomes white, while the water is reddened by the extracted particles of color.” The phlogistic crust thus corresponds in large part to the bleached-out coagulum; the difference between them is only quantitative (that is, it lies in the amount of coloring material that each contains) and not qualitative, as supposed by the humoral theory.

Microscopic examination of a clot of coagulum also enabled Malpighi to observe, as separate components, the interlacing white fibers that arise from the conglutination of much smaller but similarly shaped filaments (a process similar to that which occurs in the crystallization of salts) and the red fluid that fills the interstices of these meshes of fibers. With the microscope Malpighi could perceive that the red fluid was composed of a host of red “atoms”; it is thus clear that the discovery of the red corpuscles—although variously attributed by a number of authors who would seem to be unaware of their unmistakable description in the De polypo cordis —is surely Malpighi’s

Malpighi was able to utilize even a morbid deviation such as the heart polyp toward an investigation of a normal phenomenon. He studied aberrations to cast light upon normal organisms. In the same way, he studied simple animals to understand more complex ones, writing that the

study of insects, fish, and the first unelaborated outlines of animals has been used in this century…to discover much more than was achieved by previous ages, which limited their investigations to the bodies of perfect animals only.

Having stated this methodological formulation, Malpighi applied it in his work on the silkworm, De bombyce (London 1669), and in the latter embryological and botanical works that were edited by the Royal Society for publication in London in the 1670’s.

Malpighi was led to do embryological research through an analogy with the artisan who “in building machines must first manufacture the individual parts, so that the pieces are first seen separately, which must then be fitted together.” as he asserted in De formatione pulli in ovo (1673). In de bombyce, he had carefully observed the artisan nature construct each of the three stages—larva, chrysalis, and moth—through which the silkworm is formed. He further remarked on the specific apparatuses with which the silkworm is provided, among them the air ducts (tracheae) and the blood duct with a number of pulsating centers (corcula).

With the De formatione and the subsequent appendix to it (1675), Malpighi brought a fine structural content to embryology, which became a valuable aid to illustrating the morphology of the adult. So, too, the study of lower forms of life clarifies the morphology of more highly developed ones. Malpighi noted that the study “of the first unelaborated outlines of animals in the course of development” is particularly fruitful because the artisan nature forms them separately before combining them with one another. In the embryo, for example, the miliary glands, which will merge to form the liver, are still distinguishable as the cecal sacs (which in crustaceans remain distinct). From this point on, the paths of embryogenesis and phylogenesis were destined to cross.

The chick fetus develops in a manner similar to that of the plant embryo contained within a plant seed: from being enveloped at the start, it simultaneously “evolves” and grows in size as a result of the influx of food (yolk and albumen) liquefied by the warmth of the nest or by the fermentation process set in motion by fecundation. This notion, that embryogenesis consists of the development of constituents that in some sense existed prior to incubation, but which are nevertheless secondary to fecundation (see Adelmann), since they are induced by the “colliquamentum” of the pellucid area by the aura—or spiritous emanation —of the male seed, gave fuel to the doctrine of pre-formation, which then became a strong alternative to the traditional doctrine of epigenesis.

Malpighi’s chief embryological discoveries were the vascular area embraced by the terminal sinus, the cardiac tube and its segmentation, the aortic arches, the somites, the neural folds and the neural tube, the cerebral vesicles, the optic vesicles, the protoliver, the glands of the prestomach, and the feather follicles.

Malpighi clearly stated his comparative method in the introduction to Anatomes plantarum idea (1675):

The nature of things, enveloped in shadows, is revealed only by the analogical method [“cum solo analogismo pateat”]. Hence the necessity to follow it entirely, so as to be able to analyze the most complex mechanisms by means of simpler ones that are more easily accessible to the experience of the senses. It is the most important and most perfect things, however, that are the most immediately attractive to human genius, since they are the most necessary to human utility and therefore most worthy of consideration.

This had been true in the early work of even Malpighi himself. With youthful ardor, he had flung himself into the investigation of higher animals,

…but these, enveloped in their own shadows, remain in obscurity; hence it is necessary to study them through the analogues provided by simple animals [“simplicium analogismo egent”]. I was therefore attracted to the investigation of insects; but this too has its difficulties. So, in the end, I turned to the investigation of plants, so that by an extensive study of this kingdom I might find a way to return to early studies, beginning with vegetant nature. But perhaps not even this will be enough, since the yet simpler kingdom of minerals and elements should take precedence. At this point the undertaking becomes immense, and absolutely out of all proportion to my strength.

If Malpighi retreated before the demands of making a systematic study of minerals, he nonetheless undertook the study of plants with extraordinary success. Anatome plantarum, which appeared in London in two parts (1675 and 1679), earned him acclaim (along with Nehemiah Grew) as the founder of the microscopic study of plant anatomy. In his investigation Malpighi found that plants also have a mechanical structure: he described their ducts (some of which he compared to the tracheae of insects) and their basic “cellular” structure (an aggregate of “utricles”), which Hooke had already described (as “cellulae” in the Micrographia.

In his later studies Malpighi used the “Microscope of nature” as it was manifest in natural anomalies, and in particular in monstrosities and pathological aberrations. For example, he investigated warts and found the dermic papillae to be strikingly enlarged. Anomalous structures may be not only enlarged but also so arranged as to clarify individual components in the normal state. Thus, in onychogryphosis the lamellar structure of the normal nail is apparent; while in the jugular horn of a calf the reinforced projections of the papillae stand out, whereas in the normal horn they are concealed.

The correspondence between normal and anomalous horn is not only structural, but also morphogenetic, since the metamorphosis of the cutaneous strata into the horn is caused by mechanical stimulation. Under normal conditions this stimulation is exerted by the bony excrescence of the frontal bone: in the jugular horn it is the result of the irritation of the yoke and of the resulting saccate accumulation of fluid in the subcutaneous tissue. Malpighi adduced a similar mechanical morphogenesis in the polycystic kidney: the glandular follicles (Malpighi’s corpuscles) appear enlarged and distinct in this condition because they have been dilated by urostasis secondary to a blockage of the outflow channels. Similarly, in the nodules of the cirrhotic liver, the hepatic follicles are enlarged by the “microscope of nature,” as are lymphatic follicles that have been altered by disease (usually tuberculosis).

In De polypo cordis and subsequent treatises it is possible to identify explicit references to pathological material obtained during autopsy. Malpighi recognized the importance of local lesions, and his pathological investigations were considerably enhanced by the microscopic anatomy of the 1660’s, of which he himself was the most important investigator. The discovery of minute functional mechanisms, which in the aggregate give rise to the vital event, gave abnormal structures an added significance. The anatomical investigation of the breakdown of any of these mechanisms—even if only in such macroscopic equivalents as the lesions visible in the dissecting room — demonstrated the effect of such disturbances on the economy of the organism as a whole. Such clinical manifestations are proportional to the place and nature of the lesion; subtle anatomy thus gave rise to the anatomical investigation of the causes and localizations of disease (to paraphrase the title of the later work of Morgagni).

In his medical anatomy (or practical anatomy, as it was then called), in his emphasis on those aspects of anatomy proper to medical practice, and above all, in his use of anatomoclinical parallelism, Malpighi shaped the work of at least two generations. His pupils included Albertini and Valsalva; the De sedibus et causis morborum per anatomen indagatis of their pupil Morgagni represents a most important continuation of Malpighi’s work.

Malpighi also made considerable contributions to vegetable pathology. In particular he made a study of plant galls, which he found to be a morbid alteration of the structural plan of the infested plant. Finally, Malpighi wrote an important methodological work, De recentiorum medicorum studio, in which he supported rational medicine against the empiricists. Rational medicine was also the basis for his many Consultationes, which attest to the medical practice that he carried out concurrently with his biological researches.

BIBLIOGRAPHY

I. Original Works. Malpighi’s most important works are De pulmonibus observationes anatomicae (Bologna, 1661); De pulmonibus epistola altera (Bologna, 1661); Epistolae anatomicae de cerebro, ac lingua … Quibus Anonymi accessit exercitatio de omento, pinguedine, et adiposis ductibus (Bologna, 1665); De externo tactus organo anatomica observatio (Naples, 1665); De viscerum structura exercitatio anatomica … Accedit dissertatio eiusdem de polypo cordis (Bologna, 1666); Dissertatio epistolica de bombyce (London, 1669); Dissertatio epistolica de formatione pulli in ovo (London, 1673); Anatomes plantarum pars prima. Cui subjungitur appendix iteratas et auctas de ovo incubato observationes continens (London, 1675), which is prefaced by Anatomes plantarum idea, dated November 1671; Anatomes plantarum pars altera (London, 1679);“Dissertatio epistolica varii argumenti” [addressed to Jacob Spon], in Philosophical Transactions of the Royal Society of London, 14 (1684), 601–608, 630–646; Opera omnia (London, 1686; repr. Leiden, 1687); De structura glandularum conglobatarum consimiliumque partium epistola (London, 1689); Opera posthuma (London, 1697; repr Amsterdam, 1698); Consultationum medicinalium centuria prima (Padua, 1713); and Consultationm medicarum nonnullarumque dissertationum collectio (Venice, 1747), written with J. M. Lancisi.

A recent selection is Luigi Belloni, ed., Opere scelte (Turin, 1967), with an introduction containing a useful synopsis of Malpighi’s work.

II. Secondary Literature. A definitive biography is Howard B. Adelmann, Marcello Malpighi and the Evolution of Embryology (Ithaca, N. Y., 1966).

Luigi Belloni