Papilla

Papilla (pronounced puh-pil-uh)

(1) In anatomy, (1) a nipple-like protuberance on a part or organ of the body, (2) a vascular process of connective tissue extending into and nourishing the root of a hair, feather, or developing tooth, (3) any of the vascular protuberances of the dermal layer of the skin extending into the epidermal layer and often containing tactile corpuscles & (4) any of the small protuberances on the upper surface of the tongue often containing taste buds.

(2) In botany, a small fleshy projection on a plant; any minute blunt hair or process occurring in plants.

(3) In engineering and related fields, any small, nipple-like process or projection.

1400-1450: From the late Middle English, from the Latin papilla (a nipple, teat), the construct being papula (a pustule, pimple; a swelling) +‎ -illa (the diminutive nominal suffix).  Source of all was the primitive Indo-European imitative root pap (to swell).  From the anatomical beginnings, the meaning was extended to botany and mechanical engineering, the generalized meaning of a "nipple-like protuberance" attested from 1713, the sense of "a nipple of a mammary gland" documented from the 1690s.  The noun plural is papillae.

The derived forms include the noun papilloma (a tumor resembling a nipple) from 1866, a modern Latin hybrid, the construct being papilla (nipple) + the Ancient Greek oma (tumor), the adjective papillary (of, pertaining to, or resembling a nipple) from the 1660s, the noun papilledema (also papilloedema) (a non-inflammatory swelling of the optic disc) from 1908, from papilla + edema, from the New Latin edema, from Ancient Greek οἴδημα (oídēma) (swelling), from οἰδέω (oidéō) (I swell) and the noun pap (nipple of a woman's breast), a creation of the late twelfth century, a truncation of pappe, first attested in Northern and Midlands writing, probably from a Scandinavian source (not recorded in Old Norse but noted in the dialectal Swedish as pappe), from the primitive Indo-European imitative root pap (to swell), source also of the Latin papilla and the Lithuanian papas (nipple).  It’s speculative but pap is thought to be ultimately of infantile origin.

Variations of grease nipples.

Designed as entry points for lubricating oils, grease nipples are permanently installed by a threaded connection to which a grease gun attaches, the pressure supplied by the gun forcing a small captive bearing ball in the fitting to move back against the force of its retaining spring.  The valve that opens under pressure allows lubricant to pass through a channel and be forced into the voids of a bearing or whatever is to be lubricated and, when pressure ceases, the ball returns to its closed position.  The ball excludes dirt and functions as a check valve to prevent grease escaping back out of the fitting, functioning thus as a one-way, non-return valve.  The ball is almost flush with the surface of the fitting so that it can be wiped clean, reducing the debris which would otherwise be carried with the grease.  The convex shape of the fitting allows the concave tip of the grease gun to seal from many angles, yet with a sufficiently tight seal to force the pressured grease to move the ball and enter the fitting, rather than simply oozing past this temporary annular (ring-shaped) seal.  Grease nipples are commonly made from zinc-plated steel, stainless steel, or brass.

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The patent for the first grease nipple was granted in 1929.  Before grease nipples existed, bearings were lubricated in ways that tended to be maintenance-intensive and often provided less effective lubrication.  For example, a typical machinery bearing of the nineteenth and early centuries was a plain bearing with a cross-drilled hole to receive oil or grease, with no fitting at its mouth, or at best a cap or cup.  Often lubricant was delivered under no more pressure than gravity or a finger push might provide; oil flowing into the hole, grease pushed in.  While grease guns existed to feed the grease with higher pressure, fittings were not as good and didn’t seal as well as those used than today, nor were they as widely used.

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Since the 1920s, the ever-growing dissemination of sealed bearings has made the use of grease fittings less common.  Sealed bearings are lubricated for life at the factory, sealed so lubricant is not lost or contaminated by fluids or anything abrasive.  Grease nipples however are far from obsolete; much machinery is built with them because, provided what is usually minimal maintenance is attended to, this type of bearing and lubrication setup is cost-effective, simple, and long-lasting.  However, neglect of maintenance does shorten a lifespan.  Grease fittings are rarely found on today's consumer goods because maintenance-free products have more sales appeal but they still exist on many automobiles and are more common still on industrial, agricultural, and mining equipment where shaft diameters exceed ¾ inch (19 mm) and in electric motors with an output greater than about 5 kw.  Grease nipples are particularly numerous on marine engines because, in addition to providing lubrication, pumping grease into a fitting on a motor or other unit exposed to water expels moisture that would otherwise cause corrosion.  This can be of critical importance in machinery exposed to salt-water.