So that you can see if bacteria is present on the specimen and institute empirical therapy before that bacteria is cultured (24-48hrs) and hopefully save the person's life, where in some cases the patient may die before the exact strain of bacteria (and subsequently which antibiotics to prescribe) are known.

To remove the "dirty" oxide layer which slows down the burning reaction. It is a bit like removing the rust (oxide layer) off iron before reacting iron with something. Most metals, like iron and magnesium, form an oxide with exposure to air, and we call this tarnishing, corrosion, or particularly in the case of iron-based … Read more