| Haase's rule | The length of the foetus in centimeters, divided by 5, is the duration of pregnancy in months, i.e., the age of the foetus. (05 Mar 2000) |
|---|---|
| Haldane's rule | <genetics> if one of the two sexes is missing, sterile, or rare in a population of first-generation hybrids between two different species, then that sex is the heterogametic sex (has two different sex chromosomes, such as XY as opposed to XX). (09 Oct 1997) |
| Prentice's rule | Each centimeter of decentration of a lens results in 1 prism diopter of deviation of light for each diopter of lens power. (05 Mar 2000) |
| Schutz rule | The rate of an enzyme reaction is proportional to the square root of the enzyme concentration; applied specifically to pepsin within a limited range. Synonym: Schutz' law. (05 Mar 2000) |
| His' rule | The duration of pregnancy is calculated from the first day of the first omitted menstrual period; obsolete. (05 Mar 2000) |
| Huckel's rule | <chemistry> The number of depolarised 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. (05 Mar 2000) |
| Nagele's rule | Means of estimating date of delivery by counting back three months from the first day of the last menstrual period and adding seven days. (05 Mar 2000) |
| New Hampshire rule | Pioneering American test of criminal responsibility (1871): "if the [criminal] act was the offspring of insanity, a criminal intent did not produce it." (05 Mar 2000) |
| Durham rule | 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." (05 Mar 2000) |
| isoprene rule | 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"). (05 Mar 2000) |
| Ogino-Knaus rule | 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. (05 Mar 2000) |
| Trusler's rule 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. (05 Mar 2000) |
| Jackson's rule | After an epileptic attack, simple and quasiautomatic functions are less affected and more rapidly recovered than the more complex ones. (05 Mar 2000) |
| Jordan's rule | <genetics> An evolutionary rule that states that the closest genetic relatives of a given species are found very near it, but the two groups are isolated by some kind of natural barrier (such as a river) that neither species can cross easily. (09 Oct 1997) |
| Le Bel-van't Hoff rule | 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: stereoisomerism. (05 Mar 2000) |