The charcoal produced by the burning of the woods provides nutrients for reforestation.
Syphilis is transmitted through sexual actions through small cuts, for malaria, it would have to be through mixing of blood from a contaminated source to a uncontaminated source.
The eardrum is a thin flap of skin that is stretched tight like a drum and vibrates when sound hits it.
Lactic acid is a byproduct of short-term cellular respiration do to exercise, but if you mean lactose, then it's just the enzymes, that your stomach produces