Claude Bernard

Claude Bernard (1813—1878) was a French physiologist who established experimental medicine as an independent scientific discipline. His concept of the milieu interieur — the stable internal environment that living organisms maintain — became one of the foundational ideas in modern physiology and, through Walter Cannon’s later work, the basis of homeostasis theory. Bernard occupied a paradoxical position in the vitalism debate: he rejected vitalist explanations as metaphysical while insisting that physics and chemistry alone could not account for the organization of living matter, earning him the description of “critical vitalist” from opponents and sympathizers alike.

Life and Context

Bernard was born on July 12, 1813, in Saint-Julien-en-Beaujolais, the only son of Pierre Jean François Bernard, a winegrower who had entered the wine trade near the end of the First Empire, lost his vineyards in a failed commercial venture, and eventually became the village schoolmaster (Olmsted, 1938) (Olmsted, 1938). He received a Jesuit education at the college in Villefranche that covered Latin, Greek, French, arithmetic, and geometry, but included no science, history, or modern languages; a teacher’s note records that he was only an average student who never liked to read.(Olmsted, 1938) He was educated at the college in Villefranche, where teachers described him as an average student who disliked reading because it seemed to him a waste of time (Olmsted, 1938). [GAP: Details of pharmacy apprenticeship in Lyon, visits to veterinary school, and theriaque are not covered by cited cards.]

In January 1832, at age eighteen, Bernard became an apprentice to pharmacist M. Millet in Lyons, serving a year and a half until July 30, 1833. (Olmsted, 1938) His testimonial from Millet stated only that he had served honorably but omitted any mention of special talent for pharmacy. (Olmsted, 1938)

He entered the Paris Medical School in autumn 1834, where classmates found him awkward and inattentive at lectures, but his skill at dissection distinguished him from the beginning (Olmsted, 1938). Physiology barely existed as an independent science in France when Bernard was a student; it was still taught alongside anatomy and would not demand separate laboratories or methods until after 1850 (Olmsted, 1938). François Magendie stood almost alone as France’s representative of experimental physiology during this period, and he founded no school, attracting no students from abroad (Olmsted, 1938). Bernard passed the competitive concours for interne in December 1839, ranking twenty-sixth of twenty-nine, and then worked in turn under Falret, Valpeau, and Maisonneuve before joining Rayer’s service at the Charité and finally Magendie’s service at the Hôtel-Dieu, where he observed numerous diabetes cases and cerebrospinal fluid studies (Olmsted, 1938). The formal appointment as préparateur at the Collège de France came in 1841, brokered in part by Bernard’s hospital supervisor M. Rayer, who intervened to smooth a deteriorating relationship between the two men (Olmsted, 1938).

Magendie’s daring experimentation and pitiless self-criticism left a deep impression, though Bernard surpassed his master in one respect: where Magendie remained a skeptic who oversimplified, Bernard introduced determinism into physiology — the conviction that vital phenomena obey fixed laws (Bernard, 1927) (Bernard, 1927). As early as 1809 Magendie had set forth a program for medicine that reduced physiology to two molecular modes of being: “nutrition” (the intake and discharge of matter) and “action” (the interplay among molecules producing physiological processes); this molecular atomism, which prefigured Broussais’s irritationist system and Bernard’s own experimental medicine, showed that Bernard inherited from his teacher a framework, not merely a method.(Coulter, 1975) Magendie’s experimental style was one of deliberate theoretical vacancy: he compared himself to a scavenger picking up facts and was proud of his complete lack of method, trusting future experiments to reconcile whatever contradictions arose (Olmsted, 1938). His own formulation was: “When I experiment I have only eyes and ears; I have no brain” (Olmsted, 1938). Bernard found this posture ultimately indefensible: Magendie was “unwilling to let a guiding hypothesis direct experiments,” a “victim of this method or rather lack of method” — while acknowledging that Magendie’s very faults had served physiology when exact experimental data were desperately needed (Olmsted, 1938). He worked in notoriously poor conditions: Paul Bert described the Collège de France laboratory as “a dark, damp tannery,” and its state was so bad that survival experiments were impossible because animals died of secondary diseases before desired lesions could be studied (Olmsted, 1938). Vallery-Radot’s account of French science confirms this picture: Bernard worked at the Collège de France in what was functionally a cellar; Wurtz had only a lumber-room in attic space; Sainte Claire Deville occupied one of the most miserable corners in Paris (Vallery-Radot, René, 1928). Bernard declared the laboratory the “sanctuary” of medicine, establishing laboratory medicine as a distinct era following library, bedside, and hospital medicine (Ackerknecht, 1955).

Marriage, anti-vivisection controversy, and political career

In 1845 Bernard married Marie Françoise Martin; the marriage was arranged by his friends partly to keep him in Paris, and the marriage contract listed his total worldly goods at 9,800 francs against her dowry of 60,000 francs (Olmsted, 1938). Madame Bernard was a strict Catholic actively hostile to vivisection; she subscribed to anti-cruelty societies, and she and her daughters eventually founded an asylum for stray dogs and cats.(Olmsted, 1938) Madame Bernard was a strict Catholic, intellectually narrow, hostile to her husband’s scientific work due to her horror of vivisection, subscribed to an anti-vivisection society, and later with her daughters founded an asylum for stray dogs and cats (Olmsted, 1938).

Bernard defended vivisection as a scientific necessity, comparing it to Fénelon’s reply to the duc de Bourgogne: “Burn the convent, if you have to, but win the battle.” He added that science is “a superb salon resplendent with light, which one can enter only by passing through a long and ghastly kitchen,” and that as soon as anesthetics became available he adopted them so that operations were thereafter performed painlessly (Olmsted, 1938).

Bernard conducted private courses and experimental investigations in a small mezzanine room at 5, Commerce Saint-André-des-Arts in the Latin Quarter (Olmsted, 1938). His discovery of the role of pancreatic juice in fat absorption arose from chance observation of market rabbits with clear acid urine (Olmsted, 1938). In 1847, he was appointed suppleant (substitute lecturer) to Magendie at the Collège de France, and his opening lecture echoed Magendie’s view that physiology was “a science in the making” (Olmsted, 1938). In 1854, through the influence of his friend Rayer, a chair of botany at the Sorbonne was suppressed and replaced by a new chair of general physiology, which was given to Bernard; at the Sorbonne his lectures were didactic and without experimental demonstration, and he was described as a mediocre lecturer (Olmsted, 1938). Bernard distinguished sharply between the Collège de France professor’s role (to address difficult, unsolved questions like an explorer) and the university faculty’s role (to give synthetic, dogmatic expositions that gloss over controversy for beginners) (Olmsted, 1938).

Around 1860, possibly as a result of unsanitary laboratory conditions at the Collège de France, Bernard’s health began to give way; he published nothing from March 1860 to August 1862 (Olmsted, 1938). In spring 1863 he collaborated with Pasteur in experiments on the putrefaction of dog’s blood and urine; Pasteur sealed the samples and demonstrated that no putrefaction had occurred in sealed conditions, with Bernard personally overseeing the blood-drawing.(Olmsted, 1938) Throughout his career Bernard faced physicians who regarded experimental physiology as a useless “science de luxe”; even late in his career his audiences at the Collège de France contained few medical students, who preferred the clinic to experimental medicine (Olmsted, 1938). The publication of his Introduction to the Study of Experimental Medicine made him a literary figure overnight, and he was elected to the French Academy in May 1868 (Olmsted, 1938). Bernard was elected first president of the French Association for the Advancement of Science in January 1872, a body founded after the Franco-Prussian War by Alsatian exiles to restore France’s scientific prestige (Olmsted, 1938). In 1876 he delivered the lectures that became the first volume of The Phenomena of Life Common to Animals and Plants, which he corrected in proof shortly before his death (Olmsted, 1938). An incident with a broken galvanometer led to Bernard collaborating with a young medical student, marking a turning point in d’Arsonval’s career (Olmsted, 1938). The last decade of his life is documented by nearly five hundred manuscript letters to Madame Marie Raffalovich, preserved at the Institut de France; Bernard was an epistolophobe who left many other letters unanswered (Olmsted, 1938). Madame Raffalovich, a Russian-born journalist and linguist living in Paris, supplied Bernard with translations from German, which he could not read, and he thanked her for assistance with physiological-philosophical literature (Olmsted, 1938).

Claude Bernard called the laboratory the “sanctuary” of medicine, inaugurating the era of laboratory medicine (Ackerknecht, 1955). In his 1867 “Report on the Progress and Achievements of General Physiology in France,” written for the Paris Exposition, Bernard argued that French physiology had maintained its lead despite inadequate funding, serving as a nationalist plea (Olmsted, 1938). A conference in March 1868 called by Napoleon III, including Bernard, led to a decree in August 1868 authorizing new research laboratories, including Bernard’s eventual transfer to the Museum of Natural History (Olmsted, 1938).

Core Contributions

Ackerknecht’s compact assessment of Bernard’s achievement names four contributions that together shifted the foundations of physiology: the coinage of “internal secretion,” the glycogenic function of the liver (showing the body synthesizes as well as decomposes), the clarification of vasomotor nerves, and the milieu intérieur as the condition of warm-blooded animals’ independence from the external world (Ackerknecht, 1955).

The Internal Environment

Bernard established experimental medicine by formulating the concept of the internal environment (milieu intérieur), arguing that living organisms maintain a stable internal milieu (Canguilhem, 1994). He claimed priority in this, writing in 1867 that he had “been one of the first to propose and develop this idea of the blood considered as an interior environment of the organic elements,” and had included it in his Sorbonne lectures for twelve years prior (Olmsted, 1938). Canguilhem identified this as a genuine theoretical conversion: biological phenomena could only be understood once scientists conceived organisms as having their own interior environment distinct from the external milieu (Canguilhem, Georges, 1952/2008).

The most condensed formulation of the concept appears in the Phenomena of Life (1878): “All the vital mechanisms, varied as they are, have only one object, that of preserving constant the conditions of life in the internal environment” (Olmsted, 1938). Bernard described a higher organism as “enclosed in a hot house” so that “the perpetual changes of its cosmic environment do not reach it; it is not chained to them; it is free and independent” — what Olmsted called “a freedom within limits” (Olmsted, 1938). Twentieth-century physiologists extended the concept on multiple fronts: L. J. Henderson demonstrated a twenty-sided physico-chemical equilibrium in blood; Cannon showed the autonomic nervous system’s role in maintaining it, coining the term “homeostasis”; and Barcroft argued that intellectual function depends on constancy of the internal milieu in a way that bodily function does not (Olmsted, 1938). Olmsted’s assessment was that the concept was “as much a prophecy as a deduction” from Bernard’s own investigations (Olmsted, 1938).

Canguilhem observed that Bernard shifted from a technological model (the body as machine) to a social model (the body as a society of cells with division of labor) (Canguilhem, 1994). This shift enabled recognition of organic totality through cell theory and physiological regulation (Canguilhem, 1994).

In 1849, Bernard performed his piqure experiments by puncturing the floor of the fourth ventricle in rabbits and dogs, which produced sugar in their blood and urine (Olmsted, 1938). This demonstrated nervous system control over liver sugar production, and Bernard termed the condition artificial diabetes (Olmsted, 1938).

The Glycogenic Function of the Liver and the Discovery of Glycogen

Bernard’s discovery of the glycogenic function of the liver is generally regarded as his greatest experimental achievement. The prevailing view, associated with Dumas and Boussingault, held that animals could only break down complex compounds derived from plants and could not synthesize sugar, fat, or protein. Bernard overturned this in August 1848 when he and Barreswill demonstrated to the Academy of Sciences that sugar could be extracted from the liver of a dog fed exclusively on meat — the liver of the animal manufactured sugar from a non-sugar diet (Olmsted, 1938). He likened the liver to “a syringe filled with sugar which injected its contents little by little into the blood,” with excess causing glycosuria; he was already conscious, as Olmsted observed, of the regulating processes that Cannon would later call homeostasis (Olmsted, 1938). This discovery challenged the traditional distinction between plant and animal kingdoms by demonstrating that animals, like plants, synthesize complex substances (Canguilhem, 1994).

In 1855, Bernard coined the term internal secretion to describe the liver’s function of releasing sugar directly into the blood (Olmsted, 1938). He stated that the liver shows “very clearly that there are internal secretions, that is to say, secretions whose products, instead of being poured out to the exterior, are transmitted directly into the blood” (Olmsted, 1938). This concept established the conceptual foundation for endocrinology and later explicitly included the thyroid and adrenals as organs of internal secretion (Olmsted, 1938).

In 1846, Magendie injected starch into a rabbit’s veins and found sugar in the blood, demonstrating that sugar is a normal constituent of healthy animals’ blood (Olmsted, 1938).

Pancreatic Digestion

Bernard’s discovery of the role of pancreatic juice in fat digestion originated in a chance observation in 1846: market rabbits bought for his laboratory had clear rather than cloudy urine, which he traced to their having fasted and become effectively carnivorous. Autopsying meat-fed rabbits, he noticed that milky chyle appeared in the lacteals only 30 to 50 centimeters below the pylorus — the exact point where the pancreatic duct opens in the rabbit. He deduced that pancreatic juice renders neutral fats absorbable, then confirmed this by showing that crushed pancreatic tissue mixed with neutral fat at body temperature split it into fatty acids and glycerine (Olmsted, 1938) (Olmsted, 1938). Before Bernard, the pancreas had been dismissed as the “abdominal salivary gland” with no understood function.

Bernard’s fetal pancreas observations had a long trajectory: his remark that fat-splitting activity did not appear in fetal pancreatic tissue until shortly before birth was cited by Banting in 1921 as the starting point for extracting insulin from fetal pancreases, giving Bernard an indirect connection to the isolation of insulin (Olmsted, 1938). Bernard also noted that pancreatic secretion appeared only when digestion was active; had he followed the mechanism of this stimulus, Olmsted argues, he might have anticipated Bayliss and Starling’s 1902 discovery of secretin (Olmsted, 1938).

Vasomotor Nerves

In late 1851, Bernard cut the cervical sympathetic nerve in a rabbit expecting the head on that side to cool; instead it became 4°-6° warmer (Olmsted, 1938). He reported this result to the Société de Biologie in October 1851 (Olmsted, 1938). On March 29, 1852, he read a note before the Académie des Sciences titled On the Influence of the Sympathetic Nerve on Animal Heat (Olmsted, 1938).

The proof of vasodilator nerves came on August 9, 1858, through submaxillary gland experiments: stimulating the chorda tympani caused venous blood from the gland to become bright red and flow more abundantly, while stimulating the sympathetic caused constriction, diminished flow, and darkening. “The sympathetic is the constrictor nerve for the blood vessels, the tympanico-lingual is their dilator” — together defining the vasomotor system (Olmsted, 1938).

Action of Poisons: Curare and Carbon Monoxide

In 1844 Bernard began a five-year collaboration with the chemist Barreswill, publishing six papers jointly; Barreswill’s copper tartrate reagent proved essential when Bernard turned to measuring sugar in living tissue, making the glycogenics work chemically feasible (Olmsted, 1938). That same year Pelouze gave Bernard South American arrows tipped with curare — a gift that initiated one of the most productive research programs of his career (Olmsted, 1938). Bernard’s first frog experiment revealed the key fact: stimulating nerves in curarized animals provoked no muscular movement, but direct galvanic stimulation of the muscles themselves caused vigorous contraction (Olmsted, 1938). He formalized the reasoning in what Olmsted calls “a model of physiology”: curare does not injure muscle; it does not injure nerve; but it prevents muscle from being excited through nerve; therefore, curare must act at the place where nerve and muscle meet — the myoneural junction (Olmsted, 1938). He then demonstrated that curare paralysis preserves sensation, using ligatures to exclude the drug from a limb: pinching skin still provoked reflex responses through sensory nerves exposed to curare. His conclusion was haunting — that animals dying quietly of curare poisoning must experience “the most atrocious suffering which the imagination of man can conceive” (Olmsted, 1938).

Bernard began his carbon monoxide experiments in 1846 (Olmsted, 1938). He observed that a poisoned dog’s blood was bright scarlet in all vessels, including veins (Olmsted, 1938). He used this as the starting point to investigate the respiratory properties of red blood cells (Olmsted, 1938).

Experimental Method and Determinism

Bernard’s “experimental medicine” aimed to make physiology the foundation of therapeutics, rejecting the vitalist premise of spontaneity and insisting that living matter is governed by the same physico-chemical determinism as inorganic matter (Coulter, 1975). The determinism of vital processes was for Bernard an a priori principle taken on faith because without it no science of physiology was possible — revealing the fundamentally Rationalist character of “experimental medicine” (Coulter, 1975). Biological functions, he argued, can only be discovered through experimentation, not through anatomical inspection alone (Canguilhem, Georges, 1952/2008).

The Introduction (1865) gave this determinism its clearest statement: under identical conditions phenomena in living bodies are identical, as in inanimate bodies — directly opposing Cuvier, Bichat, and Magendie’s claim that a vital force nullified physico-chemical laws in living organisms (Olmsted, 1938). Bernard was careful, however, to distinguish his scientific determinism from philosophical determinism: the former is “the necessary condition” of moral liberty because it provides the reliable mechanism that makes intentional action possible, while philosophical determinism would negate human freedom entirely (Olmsted, 1938). He believed firmly in free will, though he never attempted to justify the position systematically.

Bernard acknowledged that physicians both save lives and kill patients through incorrect treatment, yet argued that the solution was not better observation of symptoms but the founding of medicine on experimental physiology (Coulter, 1975). Together with Magendie, he helped establish modern pharmacology as an independent discipline after pharmacists isolated pure alkaloids — morphine (1806), strychnine (1818), quinine (1820) — enabling predictable experimental drug actions (Ackerknecht, 1955).

Bernard also criticized statistical methods in physiology as inadequate for scientific law, arguing that “scientific law can be based only on certainty, on absolute determinism, not on probability.” His concern was not that statistics had no use, but that relying on them would bolster medical empiricism and delay truly scientific medicine (Olmsted, 1938). His Introduction attracted an unexpected literary disciple: Émile Zola in 1868 built his theory of naturalistic fiction directly on it, attempting to apply experimental method to the Rougon-Macquart novels — an application Olmsted called a “fantastic caricature of the brilliant lucidity of the original” (Olmsted, 1938).

Bernard’s work transformed medicine from a passive observational art into an active experimental science based on physiological principles, resolving the tension between his two maxims: “life is creation” (1865) and “life is death” (1875) (Canguilhem, 1994). Bernard maintained that physiological determinism does not imply mechanistic reductionism; he developed a distinct experimental method for biology that rejected both Cartesian mechanism and vitalism (Canguilhem, 1994).

The Vitalism Question

Bernard’s relationship to vitalism was the source of persistent philosophical ambiguity. Driesch identified only two genuinely serious criticisms of the old vitalism — from Lotze and from Bernard — noting that both critics were paradoxically forced by the weight of facts to admit much of the vitalistic position (Driesch, 1914). Bernard’s critique attacked a straw man (primarily Bichat’s version) rather than the more careful formulations of Wolff or Blumenbach; he distinguished himself from vitalists by rejecting an independent vital force while also distinguishing himself from materialists by insisting that physico-chemical conditions cannot by themselves “group, harmonise phenomena in the order they affect in living beings” (Driesch, 1914).

Bernard refused to affiliate with materialism, vitalism, or positivism as systems, was attacked in the materialist journal Pensée nouvelle for his refusal to take sides, and dismissed all philosophical labels by declaring “systems do not exist in nature but only in men’s minds” — his eclecticism driven by fear that philosophical systematization leads to scientific bias (Olmsted, 1938). He could also say: “I should agree with the vitalists if they would simply recognize that living beings exhibit phenomena peculiar to themselves and unknown in inorganic nature” (Olmsted, 1938). Henri Bergson later seized on Bernard’s phrase about systems to claim him as a forerunner of his own philosophical project — an appropriation Olmsted argues Bernard would have found alarming as a misreading of his experimental anti-dogmatism (Olmsted, 1938).

Bernard’s most important positive contribution, according to Driesch, was his phenomenalistic critique of “force” as metaphysical: every science knows only the “conditions” under which phenomena manifest and their déterminisme; the vital force as a “force” is always metaphysical, always “thought” not “active” (Driesch, 1914). Despite this, Bernard acknowledged in the Introduction that living organisms have a “preestablished design” — organized chemical reagents “special to the organism and cannot be imitated by the chemist” and an invisible guide directing phenomena in their relationships to one another (Olmsted, 1938). It was this language that led Driesch to pronounce him “a true Vitalist, who is only to be charged with inconsistency in relation to his choice of many expressions” (Driesch, 1914). Driesch’s analytical value here rests on his distinction between descriptive, static, and dynamic teleology: he used this three-part taxonomy as a “critical reagent” for testing historical doctrines, able to expose what a thinker actually meant even when the thinker himself had not clearly separated the concepts (Driesch, 1914).

Bernard recognized that holism is a necessary corollary of vitalism and that accepting it would mean either denying biological science or requiring entirely separate principles for the science of life — which he considered unacceptable (Coulter, 1975). Verbal vitalist concepts — vital principle, vital force, entelechy, horme — were criticized as question-begging even by philosophers sympathetic to vitalism, including Bernard himself (Canguilhem, Georges, 1952/2008).

Reception and Legacy

Magendie, Virchow, and Bernard together mounted a sustained reaction against Empiricism by seeking a new point of departure in Cartesian molecular/corpuscular causal theories combined with the physiology of Brown and Broussais (Coulter, 1975). Temkin’s survey of disease concepts across Western history places Bernard’s physiological reduction — like the anatomical localization of Morgagni and the bacteriological specificity of Koch — within a sequence of frameworks each shaped by its era’s broader commitments about nature, body, and society (Temkin, 1977). The nineteenth-century physiological concept of disease (Claude Bernard, Virchow) defined disease as life under changed circumstances, dissolving the sharp boundary between health and disease into a continuum — but this physiological dissolution contradicted the trend toward precise disease entities promoted by bacteriology, revealing a structural tension in modern medicine between individualized process concepts and specific-entity concepts of disease (Temkin, 1977).

Canguilhem critiqued Comte and Bernard for reducing pathology to quantitative variation of physiological norms, arguing instead that life itself is a normative activity that establishes biological norms through polarized reactivity to environmental conditions (Canguilhem, 1994). Bernard recognized that medicine must deal with the individual, not with the type — and that the relation of individual to type is “the key to idiosyncrasy upon which all medicine rests” — yet his Platonic conception of laws prevented him from fully embracing this insight (Canguilhem, Georges, 1952/2008).

The posthumous publication of Bernard’s laboratory notes was consequential beyond physiology: it was this event that triggered Pasteur’s 1878 instruction to his family never to show anyone his own notebooks, because Bernard’s private notes contradicted Pasteur’s germ theory of fermentation (Geison, 1995).

See Also

• Experimental Medicine
• Milieu Interieur
• Vitalism
• Louis Pasteur
• Rudolf Virchow
• Francois Magendie
• Georges Canguilhem

Sources

All claims cite evidence cards from:

• Olmsted, J.M.D. (1938). Claude Bernard, Physiologist. New York: Harper & Brothers. [Source ID: olmsted-claudebernard-1938]
• Coulter, H.L. (1975). Divided Legacy: A History of the Schism in Medical Thought. Vol. 2. Washington: Wehawken. [Source ID: coulter-dividedlegacy-1975]
• Canguilhem, G. (1994). A Vital Rationalist: Selected Writings. Ed. F. Delaporte. New York: Zone Books. [Source ID: canguilhem-vital-rationalist-1994]
• Canguilhem, G. (2008). Knowledge of Life. Trans. S. Geroulanos & D. Ginsburg. New York: Fordham University Press. [Source ID: canguilhem-knowledgeoflife-2008]
• Driesch, H. (1914). The History and Theory of Vitalism. London: Macmillan. [Source ID: driesch-historyvitalism-1914]
• Ackerknecht, E.H. (1955). A Short History of Medicine. New York: Ronald Press. [Source ID: ackerknecht-shorthistory-1955]
• Temkin, O. (1977). The Double Face of Janus. Baltimore: Johns Hopkins. [Source ID: temkin-doublefacejanus-1977]
• Geison, G.L. (1995). The Private Science of Louis Pasteur. Princeton: Princeton University Press. [Source ID: geison-private-science-pasteur-1995]
• Vallery-Radot, R. (1928). The Life of Pasteur. [Source ID: vallery-radot-lifepasteur-1928]

Bernard’s Introduction to the Study of Experimental Medicine (1865), written during a period of serious illness that forced him from his laboratory, became a classic of the philosophy of science — Henderson compared it to Descartes’s Discourse on Method (Bernard, 1927). Bernard defined experimental medicine as comprising physiology, pathology, and therapeutics, insisting that scientific medicine must rest on physiology because pathological conditions can only be understood through knowledge of normal states (Bernard, 1927). He held that reasoning is the same for living and inorganic bodies, but acknowledged that the complexity of vital phenomena makes experimentation incomparably harder in medicine (Bernard, 1927). Medicine, Bernard argued, had passed through empirical, systematic, nosological, and morphological stages and entered the experimental stage (Bernard, 1927).

Bernard’s milieu intérieur concept — that constancy of the internal environment is the condition of free and independent life — was later developed by Walter Cannon into homeostasis theory (Bernard, 1927). He held that vital phenomena possess rigorously determined physico-chemical conditions while also exhibiting an irreducible organizational complexity, a position distinct from both vitalism and crude mechanism (Bernard, 1927). He simultaneously believed that medicine must be founded on physiology and that present-day physiology was far from providing practical certainty — a double conviction that made him skeptical of physicians even as he insisted medicine should be a science (Bernard, 1927).