Irritability

Irritability is the property of living tissue to respond to stimulation by changing its state — contracting, secreting, or otherwise reacting without requiring direction from the soul, the will, or the central nervous system. The concept has one of the longest and most contested histories in Western physiology. It was first named by Francis Glisson in 1654, experimentally systematized by Albrecht von Haller in the 1750s, universalized by Broussais in the 1820s, and remains embedded in modern physiology under different names. At each stage, irritability was simultaneously a physiological observation and a philosophical weapon: whoever controlled the definition controlled the boundary between mechanism and vitalism.

Ancient and Medieval Origins

The Hippocratic authors had no explicit concept of irritation, but they admitted a consent among the organs attributed to an internal principle — the enormon or impetum faciens (Broussais, 1831). Galen’s doctrine of irritation was irreducibly ambiguous: his On the Use of Parts suggested nerves were necessary for organ-sensation, while his Platonic commentary attributed to plants a perception without nerves (Temkin, 1977).

Vesalius distinguished two kinds of natural motion in the body: motions serving nutrition, effected by an immanent force implanted in every part without fibres, and motions serving other parts, effected by contractile fibres (Temkin, 1977). Temkin identifies this recognition of a “force simply implanted in the parts” as anticipating later doctrines of tissue irritability (Temkin, 1977).

The sixteenth-century debate over specific cathartic drugs reveals an explicit progression within Galenism from attraction by “similitude of substance” toward irritation of the expelling faculty: Fernel retained attraction; Joubert replaced it with antipathy; Erastus used pure irritation. Temkin traces an intellectual lineage from this debate through Harvey and Van Helmont to Glisson’s concept of biological irritability (Temkin, 1977) (Temkin, 1977).

Glisson and the First Theory of Irritation

Francis Glisson’s Anatomia hepatis (1654) already contained the key elements of the irritation doctrine: sensitized parts react to distension or acridity by contraction and discharge (Temkin, 1977). His later Tractatus de natura substantiae energeticae (1672) went further, proposing that matter itself possesses primordial natural perception, appetite, and motion — a claim that led Ralph Cudworth to accuse him of hylozoism (Wolfe, Charles T., 2010-2015).

Temkin corrects a persistent error: Haller attributed the word irritabilitas to Glisson’s 1677 Tractatus de ventriculo, but the noun actually appears in the 1654 Anatomia hepatis and was used by Apuleius in the second century AD (Temkin, 1977). Haller, who grudgingly acknowledged Glisson’s priority, did his best to disqualify him as merely a metaphysician rather than an experimentalist (Wolfe, Charles T., 2010-2015).

Harvey’s concept of irritation was intermediate between Caesalpinus and the mature Glisson: Harvey distinguished a “natural sense of touch” not communicated to the sensorium commune, placing tissue-responsiveness below the threshold of consciousness (Temkin, 1977).

Broussais also credited Glisson with proposing the first theory of irritation proper, noting that Glisson ascribed to each animal fibre a property he termed irritability, “of which the results are perception and desire” (Broussais, 1831). Van Helmont contributed the “first notions clearly expressed of Irritation,” according to Broussais (Broussais, 1831). Pagel identifies close conceptual kinship between Van Helmont’s monist view of form immanent in matter and the tissue-irritability doctrines of Harvey and Glisson (Pagel, Walter, 1982). For Van Helmont, pain expressed the “boiling, seething or raging” (aestus) of the sensitive soul at irritation, and inflammation was itself the “fury, indignation or disturbance” of the vital principle resident in the affected tissue (Pagel, Walter, 1982) (Pagel, Walter, 1982).

Haller’s Experimental Systematization

Albrecht von Haller transformed irritability from a philosophical concept into an experimentally verified physiological property. Through systematic testing of every bodily tissue for its response to stimulation, he established that irritability (contractility) was the primary quality of muscle, while sensibility was the exclusive attribute of nerve (Ackerknecht, 1955). He showed irritability was inherent in all muscular fibres, independent of any super-added soul (Porter, 1997).

The experiments were aimed directly at refuting Georg Ernst Stahl’s Anima. Haller argued that the body’s contractile capacities were immanent properties of matter, comparable to attraction and gravity (Coulter, 1975). French places Haller in the defence of mechanistic orthodoxy against animists like Robert Whytt, who attributed muscular contraction to a sentient soul. Haller attributed it instead to a God-given vis insita (French, 2003).

Coulter argues that the word “irritability” was introduced twice to serve the same strategic purpose: first by Glisson to reduce Van Helmont’s Archeus, and later by Haller to reduce Stahl’s Anima. In both cases, the effect was to hypostatize the vital force into a material property and eliminate autonomous purposiveness from physiology (Coulter, 1975).

Haller’s achievement, as Temkin frames it, was freeing irritability from both anthropomorphic and mechanistic models. The anthropomorphic language of earlier writers — irritation as “indignation,” “fury,” or “appetite” — was not naive but rational given their framework; Haller’s contribution was to define the property in purely operational terms (Temkin, 1977).

Yet Driesch criticized Haller’s limitations: his rejection of Caspar Friedrich Wolff’s vis essentialis rested on the argument that it failed to explain type-specificity across species, but Haller’s own preformationism was equally unsupported. His irritability and contractility concepts could not constitute a real account of vital autonomy (Driesch, 1914).

Haller’s Restriction and Broussais’s Universalization

Haller restricted irritability to muscular fibre alone, assigning sensibility exclusively to nerves and leaving all other tissues with nothing more than a vis inertiae (Broussais, 1831). Broussais challenged this restriction directly: “Haller confined this property to the muscular fibre: it is now agreed, that it belongs to every tissue” (Broussais, 1831).

Broussais built an entire pathological system on the universalization of irritability. He defined irritation as the state produced when modifiers increase the irritability or sensibility of living tissues beyond their normal regular degree (Broussais, 1831). He distinguished irritability (a property of every tissue, including vegetable) from sensibility (requiring a nervous apparatus with a brain as centre) (Broussais, 1831), and established a terminological hierarchy: excitation or stimulation is normal physiological action; irritation is pathological excess of stimulation (Broussais, 1831). Sensibility was a consequence of irritability, not its cause: one must be irritable before being sensible (Broussais, 1831).

Broussais rejected “organic sensibility” as a superfluous abstraction (Broussais, 1831) and identified four principal forms of irritation visible to the senses: inflammatory, hemorrhagic, sub-inflammatory, and nervous (Broussais, 1831). The stomach, being “more irritable than elsewhere” among the viscera, was the most common primary seat of disease (Broussais, François-Joseph-Victor, 1832). A physician who did not know how to manage the irritability of the stomach, Broussais declared, would not know how to treat any disease (Broussais, François-Joseph-Victor, 1832). He was careful to distinguish the therapeutic consequences: when the sensibility and irritability of the stomach were much augmented, all stimulants became injurious and could precipitate functional failure; when the stomach was not inflamed, stimulation remained necessary to maintain the sympathies it awakened in other organs (Broussais, François-Joseph-Victor, 1832).

Kielmeyer’s Five Forces

Carl Friedrich Kielmeyer’s lecture Ueber die Verhältnisse der organischen Kräfte (1793) brought irritability and sensibility together within a broader taxonomy of organic powers. Kielmeyer distinguished five different organic forces: (1) sensibility, or the ability of the nerves to retain representations; (2) irritability, or the ability of muscles and other organs to respond to stimulation through contraction; (3) reproductive force (Reproductionskraft), the ability to restore injured parts or produce a new individual; (4) secretive force, the ability to deliver different juices to the right places; and (5) propulsive force, the ability to move fluids through vessels, especially in plants.(Richards, Robert J., 2002) He proposed as a general law governing sensibility that “the number of sensory modalities decreases in the series of organization as the acuity and refinement of the remaining modalities in the limited sphere increases” — thus worms lack eyes and ears but have an exquisite sense of touch.(Richards, Robert J., 2002) All of these forces could be summarized in one overarching law: “The more one of these forces, from one side, increases, the more would those on the other side be reduced.”(Richards, Robert J., 2002) The Hallerian binary of irritability and sensibility was thereby embedded in a compensatory ecology of five forces, each trading off against the others across the full series of organized beings.

The Haller-Whytt Controversy

Richards’s account of the Romantic biological context restores an important dispute that preceded Kielmeyer. Haller had distinguished sensibility and irritability as the fundamental forces in organisms, holding that only nerves were sensitive: parts without nervous involvement, like tendons, should feel no pain when pricked. Hearts and other muscles reacted to nerve stimulation by contracting. Irritability was not essentially a nervous phenomenon but a property of the muscle fiber itself, ensuing from a vis insita, or resident force.(Richards, Robert J., 2002) Robert Whytt, the Scotsman who first demonstrated the reflex character of the spinal cord, disagreed. His own experiments convinced him that all the body’s organs were sensible; accordingly, sensibility was the fundamental force and irritability the derived one.(Richards, Robert J., 2002)

John Brown generalized the problem in a different direction. In his Elementa medicinae (1780) he maintained that “excitability” constituted the basic property of living bodies, encompassing reactions of “sense, motion, mental action, and the passions.” Disease resulted when stimulus and excitability were imbalanced: too strong a stimulus relative to excitability produced sthenic disease; too weak produced asthenic disease.(Richards, Robert J., 2002) Brown said he discovered these causes when treating his own gout, finding that strong drink and opium restored the health of his big toe, a feat of cure he proudly demonstrated to his surprised dinner companions.(Richards, Robert J., 2002)

Reil’s Redefinition

J. Ch. Reil proposed a vitalism of “living matter” in which the cause of organic formation lay originally in the nature of animal matter itself, specifically in “a special sort of crystallisation” (Driesch, 1914). Reil’s definition of irritability — “the quality of animal organs which causes them to change their present state through themselves when stimulated by an external agency” — was praised by Driesch as a model of logical clearness (Driesch, 1914). Where Haller’s irritability was a property attributed to specific tissue types, Reil’s was a general quality of organized matter as such.

Irritability and Vital Materialism

Wolfe argues that vitalism and materialism should not be opposed, because in the eighteenth century matter was being reconfigured to possess irreducibly vital properties — notably irritability and sensibility (Wolfe, Charles T., 2010-2015). Matter in eighteenth-century vital materialism was gradually endowed with properties associated with life (Wolfe, Charles T., 2010-2015). The concept of irritability was central to this reconfiguration: it allowed materialists to claim they were not reducing life to mechanism while allowing vitalists to claim they were not invoking metaphysical entities.

Haller’s anti-vitalist polemic was itself a form of philosophical positioning. Neuburger records Haller arguing against animism on biological grounds: if the soul governed healing, animals without rational souls would not heal spontaneously, yet they do (Neuburger, 1943). Yet the concept of vis insita that Haller proposed as an alternative to the soul was itself irreducible to known physical forces — making the boundary between his position and the vitalism he opposed less clear than he claimed.

See Also

• Albrecht von Haller
• Francis Glisson
• Broussais
• Vitalism
• Sensibility
• Nervous System
• Jan Baptist Van Helmont
• Georg Ernst Stahl

Sources

All claims cite evidence cards from:

• Richards, R.J. (2002). The Romantic Conception of Life: Science and Philosophy in the Age of Goethe. Chicago: University of Chicago Press. [Source ID: richards-romanticconception-2002]
• Coulter, H.L. (1975). Divided Legacy. Vol. 2. Washington: Wehawken. [Source ID: coulter-dividedlegacy-1975]
• Ackerknecht, E.H. (1955). A Short History of Medicine. New York: Ronald Press. [Source ID: ackerknecht-shorthistory-1955]
• Driesch, H. (1914). The History and Theory of Vitalism. London: Macmillan. [Source ID: driesch-historyvitalism-1914]
• Broussais, F.J.V. (1832). Principles of Physiological Medicine. Philadelphia. [Source ID: broussais-physiologicalmedicine-1832]
• Broussais, F.J.V. (1831). On Irritation and Insanity. Columbia, SC. [Source ID: broussais-irritation-1831]
• French, R. (2003). Medicine before Science. Cambridge: Cambridge University Press. [Source ID: french-medicinebefore-2003]
• Porter, R. (1997). The Greatest Benefit to Mankind. London: HarperCollins. [Source ID: porter-greatestbenefit-1997]
• Temkin, O. (1977). The Double Face of Janus. Baltimore: Johns Hopkins. [Source ID: temkin-doublefacejanus-1977]
• Wolfe, C.T. Various papers on vitalism. [Source ID: wolfe-vitalism-papers]
• Neuburger, M. (1943). The Doctrine of the Healing Power of Nature. New York. [Source ID: neuburger-healing-power-of-1943]
• Pagel, W. (1982). Joan Baptista Van Helmont. Cambridge: Cambridge University Press. [Source ID: pagel-vanhelmont-1982]

Editorial Notes

Gaps the encyclopaedia compiler flagged for future evidence work, collected from inline markers in the body and frontmatter.

Sources