Sunday, January 21, 2007


A lotion is a low- to medium-viscosity medicated or non-medicated topical preparation intended for application to unbroken skin. Most lotions are oil-in-water emulsions but water-in-oil lotions are also formulated. Lotions are usually applied to external skin with a clean cloth, cotton wool or gauze. The key components of a lotion emulsion are the aqueous and oily phases, an emulgent to prevent separation of these two phases, and, if used, the drug substance or substances. A wide variety of other ingredients such as fragrances, glycerol, dyes, preservatives, vitamins, proteins and stabilizing agents are commonly added to lotions.

It is not uncommon for the same drug ingredient to be formulated into a lotion, cream and ointment. Creams are the most convenient of the three but are inappropriate for application to regions of hairy skin such as the scalp, while a lotion is less viscous and may be readily applied to these areas. Lotions also have an advantage in that they may be spread thinly compared to a cream or ointment and may economically cover a large area of skin. Non-comedogenic lotions are recommended for use on acne prone skin.

Monday, January 08, 2007

Unusual Twinnings

There are some patterns of twinning that are exceedingly rare: while they have been reported to happen, they are so unusual that most obstetricians or midwives may go their entire careers without encountering a single case. Among fraternal twins, in rare cases, the eggs are fertilized at different times with two or more acts of sexual intercourse, either within one menstrual cycle or, even more rarely, later on in the pregnancy. This can lead to the possibility of a woman carrying fraternal twins with different fathers. This phenomenon is known as heteropaternal super fecundation. One 1992 study estimates that the frequency of heteropaternal super fecundation among dizygotic twins whose parents were involved in paternity suits was approximately 2.4%; see the references section, below, for more details.

Among monozygotic twins, in extremely rare cases, twins have been born with opposite sexes. The probability of this is so vanishingly small that multiples having different genders are universally accepted as a sound basis for a clinical determination that in utero multiples are not monozygotic. When monozygotic twins are born with different genders it is because of chromosomal birth defects. In this case, although the twins did come from the same egg, it is incorrect to refer to them as genetically identical, since they have different karyotypes.

Monday, January 01, 2007


Biodiversity or biological diversity is the diversity of life. There are a number of definitions and a measure of biodiversity. Biodiversity has no single standard definition. The most basic definition is "variation of life at all level of biological organization". Another definition holds that biodiversity is a measure of the relative diversity among organisms present in diverse ecosystems. "Diversity" in this definition includes diversity within a species and among species, and comparative diversity among ecosystems.

A third definition that is often used by ecologists is the "totality of genes, species, and ecosystems of a region". An advantage of this description is that it seems to describe most circumstances and present a unified view of the traditional three levels at which biodiversity has been identified.

The 1992 United Nations Earth Summit in Rio de Janeiro defined "biodiversity" as "the changeability among living organisms from all sources, including, 'inter alia', terrestrial, marine, and other aquatic ecosystems, and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems".