A reference parameter designates the caller's actual storage. Assigning through it can change what the caller subsequently observes; passing a complete independent copy would instead change only the local copy. A value parameter containing an object reference is another case: copying that reference does not copy the referenced software object.

In Oberon, a variable parameter is marked VAR and stands for the supplied actual variable. For example, a procedure accepting VAR x: INTEGER can increment the caller's integer through x.^[ref]

A read-only algorithm can use a reference parameter to avoid copying a large array, while its formal specification still prohibits writes. Reference aliasing remains relevant: two parameters can designate overlapping storage. A proof of algorithm correctness must account for the actual aliasing rules rather than assume that different parameter names denote independent values.

A parameter initialized from the actual argument's value. Whether passing an aggregate copies all elements or merely a reference is language-dependent; in whole-array copying semantics, a length-$L$ argument costs $\Theta (L)$ per call. This differs from a language that passes an object reference by value.

Evaluate argument expressions before invoking a function. A monadic interpreter must also specify the order of those evaluations when its computational monad represents effects.

Paraplegia is paralysis affecting both lower limbs, sometimes with additional lower-trunk impairment. It can result from disorders affecting the spinal cord or other relevant pathways; the level and completeness of the lesion determine which functions are affected.

Motor impairment, sensory loss and autonomic dysfunction are separate dimensions. The word paraplegia alone does not specify the presence or absence of every one of them.

Molecular oxygen in a chemical solution, distinguished from oxygen chemically bound in water molecules.

Historical term for slow oxidation, used in discussions of cellular respiration.

Loss of normal contact between the articular surfaces of an anatomical joint. It differs from a fracture, although a single injury can produce both.

A break in the continuity of a solid structure, especially a bone in clinical usage. Pattern, displacement and surrounding tissue injury determine mechanical consequences beyond the fact that a break exists.

A supporting device used to suspend or stabilize a limb. Support can reduce movement and load, but it does not itself demonstrate that a fracture or dislocation is correctly aligned.

The optic canal is the bony passage carrying the optic nerve and ophthalmic artery into the orbit. Its location differs from the superior orbital fissure used by several ocular motor nerves. This separation helps relate a local lesion to different patterns of visual and motor impairment.

The superior orbital fissure is an opening at the posterior orbit transmitting several ocular motor nerves and other structures. Relations to the common tendinous ring determine which pathways pass through or outside the ring. The nearby optic canal is a separate route.

The inferior orbital fissure is a gap in the posterior-inferior orbital wall connecting the orbit with neighboring deep facial spaces. It transmits nerves and vessels, including routes associated with the maxillary division of the trigeminal nerve. It is distinct from the superior fissure.

The periosteum lining the orbit (anatomy). In an orbital dissection, it separates the surrounding bones from the contents until opened.

A fibrous attachment at the apex of the orbit (anatomy) from which the four rectus extraocular muscles arise. Its relations distinguish structures passing through the optic canal and different parts of the superior orbital fissure.

Jean-Baptiste Biot made optical rotation a practical subject of chemical measurement. His 1845 instructions addressed both observation and quantitative measurement of rotatory optical properties, with applications to scientific, industrial and medical chemistry. In polarimetry, a polarimeter compares the orientation of transmitted polarized light with a reference. Controlling path length, wavelength, temperature and concentration makes the measured optical rotation useful for comparing samples; a rotation reading alone does not identify all these quantities independently.^[ref]

A physicist associated with optical rotation and Biot's saccharimeter.

A spectroscope makes an optical spectrum observable, commonly by passing light from an entrance slit through a collimator and an optical prism or diffraction grating. An eyepiece permits direct inspection of separated spectral lines or bands, while a recording detector makes the instrument a spectrograph.

An emission lamp gives bright spectral lines; placing an absorbing sample in front of a continuous source can produce an absorption spectrum. Slit width affects both received radiant power and the ability to distinguish neighboring features. A visible dark band must be checked against the source spectrum and instrument response before being assigned to sample absorption.

An instrument with a polarizer and an optical analyzer, often with a specimen between them, used to reveal changes of polarization through transmitted intensity. Crossed ideal elements give extinction without a polarization-changing sample.

A liquid preparation containing opium constituents. Its antidiarrhoeal action does not treat every cause of diarrhoea.

Extractum Opii is a concentrated extract of opium. Extraction changes the mixture of constituents relative to the original crude material.^[ref]