kraven

Escaping gases, movement and rough surfaces.
Your joints can make a variety of sounds: popping, cracking, grinding, and snapping. The joints that "crack" are the knuckles, knees, ankles, back, and neck. There are different reasons why these joints "sound off".

Escaping gases: Scientists explain that synovial fluid present in your joints acts as a lubricant. The fluid contains the gases oxygen, nitrogen, and carbon dioxide. When you pop or crack a joint, you stretch the joint capsule. Gas is rapidly released, which forms bubbles. In order to crack the same knuckle again, you have to wait until the gases return to the synovial fluid.
Movement of joints, tendons and ligaments: When a joint moves, the tendons position changes and moves slightly out of place. You may hear a snapping sound as the tendon returns to its original position. In addition, your ligaments may tighten as you move your joints. This commonly occurs in your knee or ankle, and can make a cracking sound.
Rough surfaces: Arthritic joints make sounds caused by the loss of smooth cartilage and the roughness of the joint surface.
Is joint cracking harmful? If you are feeling pain when your joints pop, than you should seek a health care professional. In terms of knuckle cracking, some studies show that knuckle cracking does not cause serious harm. Other studies show that repetitive knuckle cracking can do some damage to the soft tissue of the joint. It may also lead to a weak grip and a swelling hand.

The outermost layer of the skin swells when it absorbs water. It is tightly attached to the skin underneath, so it compensates for the increased area by wrinkling. However, new research is investigating the role of digital vasoconstriction (narrowing of blood vessels) of water immersion wrinkling of the skin.
There are various theories of why fingers and toes wrinkle in water. Most biologists suggest that the tough outer layer of skin made up of dead keratin cells is responsible. Keratin is a protein found in hair, nails, and the outermost layer of our skin.

Our skin is made up of three layers:

The subcutaneous tissue is the deepest layer. It contains fats and connective tissue along with large blood vessels and nerves.
The dermis is the middle layer. It contains the blood vessels, nerves, hair roots, and sweat glands.
The epidermis is the topmost layer. It helps to prevent evaporation of water from the body and to protect the internal layers from harm.
The epidermis is made up of four layers:

the stratum corneum
granular layer
squamous cell layer
and basal cell layer
The stratum corneum is the outer layer of our skin - the part that we can see and feel. This is the layer with the dead keratin cells.

While a person is in the pool or a bathtub for a long time, the dead keratin cells absorb water. This absorption causes the surface area of the skin to swell, but the outer layer is tightly attached to the living tissue. So, to compensate for the increased surface area, our skin wrinkles.

So why does this happen to hands and feet and not to other parts of the body? Because the hands and feet have the thickest layer of dead keratin cells. Our hands and feet are subjected to a lot of wear and tear. Imagine if the palm of our hands had skin as thin as that on our backs. No fun playing basketball with skin that thin!

Scientists continue to look for the exact mechanisms of why our fingers and toes wrinkle when immersed in water (Wilder-Smith et al, Hsieh et al). One theory gaining recognition is the role of digital vasoconstriction (narrowing of blood vessels). When hands are immersed in water it seems that the nerve fibers are triggered to shrink and glomus bodies (body temperature regulators in the skin) in the hand lose volume, which then pulls the skin structures downwards to produce wrinkling. Studies on patients with loss of nerve function in their hands due to a disorder or replantation of amputated fingers exhibit no or slight wrinkling in the fingers when immersed in water (Hsieh et al). As the nerve functions return, so did the wrinkling.

For more fascinating facts about the skin see the following Web sites and further reading sections.

Unstable chemicals.
Onions produce the chemical irritant known as syn-propanethial-S-oxide. It stimulates the eyes' lachrymal glands so they release tears. Scientists used to blame the enzyme allinase for the instability of substances in a cut onion. Recent studies from Japan, however, proved that lachrymatory-factor synthase, (a previously undiscovered enzyme) is the culprit (Imani et al, 2002).

The process goes as follows:

Lachrymatory-factor synthase is released into the air when we cut an onion.
The synthase enzyme converts the sulfoxides (amino acids) of the onion into sulfenic acid.
The unstable sulfenic acid rearranges itself into syn-ropanethial-S-oxide.
Syn-propanethial-S-oxide gets into the air and comes in contact with our eyes. The lachrymal glands become irritated and produces the tears!

Recent evidence suggests that some people give off masking odors that prevent mosquitoes from finding them.
Recently, scientists at Rothamsted Research in the UK discovered that some people produce chemicals that smell bad to mosquitoes, masking the chemicals that usually attract the mosquitos.

James Logan and John Pickett (Vince, 2006) devised some unique ways of testing body odor. First, they had two different people put one hand into each end of a chamber and the investigators watched which hand the mosquitoes preferred. Then they selected the person who was not preferred (who felt lucky up to this point) and sealed their body in foil to collect their sweat. Talk about an unpleasant experiment. The researchers set about analyzing the body chemicals and are now waiting to patent the results in hopes of producing a natural insect repellent.

The female mosquito is the one that bites (males feed on flower nectar). She requires blood to produce eggs. Her mouthparts are constructed so that they pierce the skin, literally sucking the blood out. Her saliva lubricates the opening. Its the saliva plus the injury to the skin that creates the stinging and irritation we associate with mosquito bites.

Unfortunately, mosquitoes are carriers for a host of diseases, including malaria, yellow fever, West Nile virus, and Dengue fever. There are hundreds of species of mosquitoes belonging to the family Culicidae. Since they breed in standing water, a way to eliminate them around the home is to remove objects where water collects, such as cans, buckets, old tires, and refreshing the water in bird baths at least once a week. Turn water barrels upside down during the winter, as well.

Insect repellents often contain DEET (N,N-diethyl-meta-toluamide) although there are more natural ingredients available, such as eucalyptus oil extract. You can try to limit your exposure to mosquitoes when outdoors by using a fan or by covering exposed skin with light colored clothing and a hat. Mosquitoes tend to be more of a problem from dusk to dawn.