How are human nails able to detect diseases>?

Illnesses can be diagnosed with the help of people's nails. Yury Zakharov, doctor of medical sciences, director of the Moscow phytotherapy center says, nail diagnostics is practiced in the traditional Chinese medicine, although it is an applied practice used in a combination with other methods. "For example, if a patient has a square nail, we examine their iris, trying to diagnose an oncological illness. As a rule, the iris examination proves it. The main advantage of such an approach is the opportunity to identify many symptoms at early stages, two or three years before a disease develops. Needless to mention that it is extremely important to people.
Nails reflect changes in internal organ

If the nail color changes, a disorder happens during the latest month. If the structure, shape, surface of nails changes, it indicates a serious chronic disease, which has been developing for several years. If a person notices such changes with nails, they have to take a profound care of their health

For more details see below website:
http://english.pravda.ru/science/health/...

a few diseases and poisonings show up in the human nail. Look up detect disease human nails on Webmd. Liver and kidney, and heart are big ones.

Diseases:
* Disorders that affect the amount of oxygen in the blood (such as abnormal heart anatomy and lung diseases including cancer or infection) may causeclubbing.
* Kidney disease can causes a build-up of nitrogen waste products in the blood, which can damage nails.
* Liver disease can damage nails.
* Thyroid diseases including hyperthyroidism or hypothyroidism may cause brittle nails or splitting of the nail bed from the nail plate (onycholysis).
* Severe illness or surgery may cause horizontal depressions in the nails (Beau's lines).
* Psoriasis may cause pitting, splitting of nail plate from nail bed (onycholysis), and chronic destruction of the nail plate (nail dystrophy)
* Other conditions that can affect the appearance of nails include systemic amyloidosis, malnutrition, vitamin deficiency, andLichen planus.
Poisons:
* Arsenic poisoning may cause white lines and horizontal ridges.
* Silver intake can cause a blue nail.
Nail biting is the habit of biting one's fingernails or toenails during periods of nervousness, stress, hunger, or boredom [1]. It can also be a sign of mental or emotional disorder. The clinical name for nail biting is chronic onychophagia.
Medical test
Health care and pre-hospital care providers (paramedics) often use the fingernail beds as a cursory indicator of distal tissue perfusion of individuals who may be in shock.
Procedure: Gently depress and release the fingernail bed with your finger. This act will briefly turn your nailbed white and normally return to a pink colour within 1-2 seconds. Delayed return to pink colour could be an indicator of certain shock states such as hypovolemia.
Please see the web pages for more details on Nail and nail abnormalities.

Nails can show : 1. Anaemia.2. Jaundice. 3. Cyanosis.
Clubbing of fingers: This is seen in congenital cyanotic heart diseases, chronic lung diseases, liver diseases and malabsorption.