Jeffrey Aronson: When I use a word . . . Diffusion

jeffrey_aronsonDiffusion and dissemination are important aspects of translational research. They are the processes whereby the products of such research—knowledge, skills, understanding, innovations—spread, encouraging implementation. Diffusion is a passive process, like the transmembrane movements of sodium and potassium down their concentration gradients, while dissemination is active, like active transport of sodium and potassium against the concentration gradient through the activity of the sodium-potassium adenosine triphosphatase (the Na/K pump). To complete the analogy, facilitated diffusion occurs when diffusion is helped on its way by the presence of a specific channel.

The word diffusion has its origin, surprisingly, in the IndoEuropean root GHEU, which meant to pour, specifically referring to a libation. The gh would have been pronounced gutturally, technically a voiceless velar fricative, as in the Irish word for a lake, “lough” (Scottish “loch”).

In Greek the digraph gh, became the guttural kh, represented by the letter χ (chi), This gave χέειν, to pour, and derivatives such as χῡμός and χῡλός, which both meant juice, typically the juice of plants, and hence flavour. Chyme is the semifluid matter to which food is converted in the stomach by the action of the gastric secretions, whence it passes into the small intestine, where it is converted to chyle by the action of other digestive juices, such as bile and pancreatic secretions. An ecchymosis, a bruise, occurs when the body’s juice, blood, pours into the subcutaneous tissues.

Many English derivatives of ἔγχῠμα (enkhuma), an infusion, describe structures of plant tissues: aerenchyma (large air filled intercellular spaces), bothrenchyma or taphrenchyma (pitted tissue in wood), chlorenchyma (green tissue due to chloroplasts), cinenchyma (vessels containing latex or milky juice), collenchyma (cells with thick walls), cylindrenchyma (cylindrical cells), inenchyma (cells resembling spiral vessels), merenchyma (loosely packed ellipsoid or spheroid cells separated by wide spaces), ovenchyma (oval cells), pinenchyma (long thin cells), pleurenchyma (vascular tissue in wood), prismenchyma (prismatic cells), prosenchyma (hard, typically woody, fibrovascular tissue), and sclerenchyma or sterenchyma (dead cells that have become lignified, also a hard substance in coral skeletons). Chondrenchyma is cartilaginous tissue in sponges. Mesenchyme is the embryonic tissue that develops into connective and skeletal tissues, including blood, lymph, and muscles. Parenchyma is the specialised functional tissue in an organ, distinct from the framework of connective tissue, the stroma; parenchymula is the embryonic stage that follows the closed blastula and also a zoological term for a sponge larva with no internal cavity.

A Greek word related to χῡμός, χυμεία, and a variant form, χημεία, meant the art of making alloys by pouring different metals together. Add the Arabic definite article, al, and you get al-kīmiyā’, in postclassical Latin alchimia, giving us alchemy and eventually chemistry.

Another Greek derivative, χοάνη, was a funnel, for pouring things. This gives us choanocytes (collar cells in the inside of sponges), the choanosome, which contains choanocytes, and the choanoderm, a layer of choanocytes. Another pourer, χύτρα, was an earthenware pot, and also a type of kiss in which the ears were held like the handles of a pot; χύτραι (plural) were large swellings in the corners of the eyes. A chytrid is a type of pot shaped fungus (order Chytridiales).

In Germanic languages the gh in GHEU simply became a g, giving us gush, gust, geyser, and gut, through which our food pours.

In Latin the gh in IndoEuropean roots generally became an h. Hiatus, for example, comes from GHᾹI, to yawn or gape, and horrible from GHERS, to bristle. However, in a few cases gh became f, in the way that some people pronounce the name van Gogh “van Goff”, instead of gutturalising the gh (and the initial g as well, as the Dutch do). So, from GHEU comes fundere, to pour, from which we get fuse and fusion, as well as futile, from futilis, meaning leaky. To fuse originally meant to melt or liquefy, i.e. to make a solid pourable, then to blend by liquefaction. An electric fuse is made of fusible metal; the electricity fuses when the fuse melts. Add almost any prefix you like to “fusion” and you get a profusion of new words, from affusion to transfusion (Box).

In postclassical Latin diffusio was watering of the eyes. In English, diffusion originally meant an outpouring of speech or writing—prolixity or verbosity—then, less dramatically, the action of spreading or dispersion. But in classical Latin diffusio [animi] was cognitive expansiveness. Just what you need for research.

Box Words derived from fusion (definitions based on those in the Oxford English Dictionary)

affusion Accumulation of blood or serum; (cold affusion) pouring cold water on; (trine affusion) baptism by immersion three times
autotransfusion Displacement of blood from the periphery of the body towards the heart and vital organs; transfusion of a person’s own blood or blood products
circumfusion Pouring or diffusion around
confusion Mental agitation; embarrassment; disorder; commotion; mistaking one thing for another
defusion A psychiatric term for reversal of the normal fusion of the instincts of life and death
diffusion The act of pouring out; spreading or dispersion of something, concrete or abstract,  throughout or over a wide area; the spontaneous molecular mixing or interpenetration of two substances, especially gases or liquids, without chemical combination
effusion A pouring out; a spilling of liquid; a shedding of tears; the escape of fluid from its normal vessel; an outpouring of feelings
electrofusion Fusion of metals or other materials by means of an electric current
flicker fusion The apparent steadiness of a regularly varying source of light when the frequency of the variation is sufficiently great
immunotransfusion Any of various techniques in which an antigen and an antibody are allowed to diffuse towards each other in a gel or other solid medium, typically forming visible or measurable lines of precipitation
inconfusion Absence of confusion
infusion The action of pouring in a liquid; the action of infusing some principle, quality, or idea, into the mind, soul, or heart; the process of pouring water over a substance, or steeping the substance in water; the liquid so produced
interdiffusion Mutual diffusion
interfusion Permeation or interspersion with an infusion or mixture of something else
microdiffusion Any of several microanalytic techniques involving diffusion
perfusion Pouring or sprinkling a fluid etc on, over, or through something; the passage of a liquid, esp. blood, through an organ or tissue
perifusion Exposure of an organ or tissue to an enveloping flow of liquid, usually buffered saline
profusion Lavish expenditure; extravagance; abundance
reaffusion Pouring something on again
rediffusion Repeated diffusion; dissemination, broadcasting, or rebroadcasting of a programme by various methods
refusion An act of pouring back; an act of refunding money; the return of the individual soul to the “anima mundi”
reinfusion Repeated infusion; autotransfusion
reperfusion Repeated perfusion; restoration of blood flow to an organ or tissue, after a period of ischaemia
self-diffusion Migration of constituent atoms or molecules within the bulk of a substance, especially a crystalline solid
semi-fusion Softening of a solid mass
suffusion Extravasation of a fluid or humour over a part of the body; a cataract
superaffusion Superfusion
superfusion Pouring liquid over something; passing a stream of liquid over the surface of a piece of tissue, to maintain its viability and to study the interchange of substances between it and the liquid; the cooling of a liquid to below its freezing point without solidification or crystallisation occurring
superinfusion Additional, extensive, or excessive infusion
surfusion Superfusion
transfusion Pouring a liquid from one vessel into another; transferring blood or constituents thereof from a person or animal into the veins of another

Jeffrey Aronson is a clinical pharmacologist, working in the Centre for Evidence Based Medicine in Oxford’s Nuffield Department of Primary Care Health Sciences. He is also president emeritus of the British Pharmacological Society.

Competing interests: None declared.