rule

rule (rul)

A criterion, standard, or guide governing a procedure, arrangement, action, etc. See also law, principle, theorem. [O. Fr. reule, fr. L. regula, a guide, pattern]
Abegg's r. the tendency of the sum of the maximum positive and maximum negative valence of a particular element to equal 8; e.g., C may have a valence of +4 and -4, O of +6 and -2. Sometimes loosely stated as all atoms have the same number of valences, a consequence of the tendency of valence electron shells to be filled to 8.
American Law Institute r. a test of criminal responsibility (1962): "a person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the wrongfulness of his conduct or to conform his conduct to the requirements of law."
r. of bigeminy r. that a ventricular premature beat will follow the beat terminating a long cycle. Sudden prolongation of the ventricular cycle, by changing the refractoriness in the conduction system, causes a peripheral region of bidirectional block to become transiently unidirectional and thus opens potential pathways for reentry to occur.
Chargaff's r. in DNA the number of adenine units equals the number of thymine units; likewise, the number of guanine units equals the number of cytosine units.
Clark's weight r. an obsolete r. for an approximate child's dose, obtained by dividing the child's weight in pounds by 150 and multiplying the result by the adult dose.
Cowling's r. an obsolete r. for a child's dose: that fraction of the adult dose obtained by dividing the age of the child at the nearest birthday by 24.
Durham r. an American test of criminal responsibility (1954): "an accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect."
Gibb's phase r. phase r
Goriaew's r. rarely used term for a r. of a blood counting field by which it is marked off in a series of squares, some of which are again subdivided into sixteen smaller ones.
Haase's r. the length of the fetus in centimeters, divided by 5, is the duration of pregnancy in months, i.e., the age of the fetus.
His' r. the duration of pregnancy is calculated from the first day of the first omitted menstrual period; obsolete.
Hückel's r. the number of depolarized electrons in an aromatic ring is equal to 4n + 2 where n is zero or any positive integer; l-tyrosine, l-phenylalanine, l-tryptophan, and l-histidine (when the imidazole ring is deprotonated) obey this rule.
isoprene r. the classical, outmoded statement that naturally occurring terpenes are built up by condensation of isoprene units by either a 1-4 linkage ("head to tail") or a 4-4 linkage ("tail to tail").
Jackson's r. after an epileptic attack, simple and quasiautomatic functions are less affected and more rapidly recovered than the more complex ones.
Le Bel-van't Hoff r. the number of stereoisomers of an organic compound is 2n where n represents the number of asymmetric carbon atoms (unless there is an internal plane of symmetry). A corollary of their simultaneously announced conclusions, in 1874, that the most probable orientation of the bonds of a carbon atom linked to four groups or atoms is toward the apexes of a tetrahedron, and that this accounted for all then-known phenomena of molecular asymmetry (which involved a carbon atom bearing four different atoms or groups). See also stereoisomerism.
Liebermeister's r. in adult febrile tachycardia, about eight pulse beats correspond to an increase of 1°C.
Meyer-Overton r. because inhalation agents act via the lipid-rich CNS cells, anesthetic potency increases with lipid solubility.
M'Naghten r. the classic English test of criminal responsibility (1843): "to establish a defense on the ground of insanity, it must be clearly proved that, at the time of committing the act, the party accused was laboring under such a defect of reasoning, from disease of the mind, as not to know the nature and quality of the act he was doing, or if he did know it, that he did not know he was doing what was wrong."
Nägele's r. means of estimating date of delivery by counting back three months from the first day of the last menstrual period and adding seven days.
New Hampshire r. pioneering American test of criminal responsibility (1871): "if the [criminal] act was the offspring of insanity, a criminal intent did not produce it."
r. of nines method used in calculating body surface area involved in burns whereby values of 9 or 18 percent of surface area are assigned to specific regions as follows: Head and neck, 9%; anterior thorax, 18%; posterior thorax, 18%; arms, 9% each; legs, 18% each; perineum 1%.
Ogino-Knaus r. the time in the menstrual period when conception is most likely to occur is at about midway between two menstrual periods; fertilization of the ovum is least likely just before or just after menstruation; the basis for the rhythm method of contraception.
r. of outlet an obstetric r. for determining whether the pelvic outlet will permit the passage of a fetus; the sum of the posterior sagittal diameter and the transverse diameter of the outlet must equal at least 15 cm if a normal-sized baby is to pass.
phase r. an expression of the relationships existing between systems in equilibrium: P + V = C + 2, where P is the number of phases, V the variance or degrees of freedom, and C the number of components; it also follows that the variance is, V = C + 2 - P. For H2O at its triple point, V = 1 + 2 - 3 = 0, i.e., both temperature and pressure are fixed.Gibb's phase r;
Prentice's r. each centimeter of decentration of a lens results in 1 prism diopter of deviation of light for each diopter of lens power.
Rolleston's r. the ideal adult systolic blood pressure is 100 plus half the age, whereas the maximal physiologic pressure is 100 plus the age; of historical interest.
Schütz r. the rate of an enzyme reaction is proportional to the square root of the enzyme concentration; applied specifically to pepsin within a limited range.Schütz' law;
Trusler's r. for pulmonary artery banding a method that gives guidance as to the correct tightness of the band; the degree of banding for a complex congenital cardiac anomaly with bidirectional shunting less than that for simple ones.
Young's r. an obsolete r. to determine a child's dose: 12 is added to the child's age and the sum is divided by the age; the adult dose divided by the figure so obtained gives the proper dose.

 

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