[ramanand]

Originally Posted by mynah

Dogs' licking their recovering (and presumably itching) body parts seems to promote healing. We are rather Johny-comes-lately primates who are more adept at using our fingers than bending down to lick whatever itches (imagine licking some of the parts your dog habitually licks in a meeting or rush hour traffic). As a result, we may represent an evolutionary offshoot that is less equipped to deal with the itching response in the natural way, and had to come up with antibiotics and antiseptics instead.

A logical reply indeed,
licking of injury by dogs really seems to be healing procees and also it is a protective process too, as the saliva contains some of the enzymes that inhibits the growth of micro organisms (such as bacteria and viruses) on the exposed injured parts which are more prone to the attack of the infectious microbes. Licking provides constant and regular cover of enzymes over the injured part,perhaps these enzymes (like lysozyme) inhibits the cross linkages of NAM and NAG with the amino sugars in the bacteria and thus inhibiting the synthesis of their cell wall, thereby reducing the chances of their survival on the wound.

[ramanand]

Pain is useful because it constantly reminds the mind to protect the injured part from getting further injury, also it makes us not to over stress the injured parts which might slow down the healing process, so during the course of evolution sensation of pain developed as a protective mechanism. But this sensation of pain reduces as wound is on the final stage of healing, but at this stage the sensation of pain transforms into the sensation of itch (due to growth of underlying tissues and nerves). To get rid off from itch we start scratching. A scratch due to constant friction causes the local increase in temperature of that area, due to increase in temperature blood circulation to that area increases in order to lower back the temperature.
With increase in temperature various cells and molecules of immune system reaches the injured site and protects the area from the attack of the infectious micro organisms. This is the protective aspect of itching which has developed in the course of evolution.