Elizabeth Martin and Robert Hine. Latest Edition (7 ed.) Fully revised and updated, the sixth edition of this dictionary provides comprehensive coverage of biology, biophysics, and biochemistry, as well as key terms from medicine and palaeontology.
For example, if someone scratches a mole until it bleeds, the resulting lesion, a crust, is now a secondary skin lesion. The most common secondary skin lesions include: 1  crust: a crust, or a scab, is created when dried blood forms over a scratched and irritated skin lesion. 2  ulcer: typically caused by a bacterial infection or physical trauma. 3  scale: patches of skin cells that build up and then fall off the skin.
âThinâ blood. Usually, blood cells flow freely through arteries to carry oxygen and nutrients to every part of the body. However, these blood cells also must be able to clump together and form a clot if we are injured. This is what happens when a scab forms over a cut.