THe dark rubbery lining you refer to impedes peristalsis with the results you describe so well .

BUT this ONLY HAPPENS because the natural happening at birth is clubbed into oblivion by antibiotics!.

When baby is born it presents a nice warm wet virgin environment for an enormous quantity of micro organisms .

These colonise this virgin land and battle for territory . Eventually they settle their differences and harmonise in order to ensure that this territory [the baby] survives and they survive with it .

Thus they act to help the body to digest many substances [ which otherwise it could not absorb] in a symbiotic operation.

When antibiotics are applied [in a totally reckless fashion] to this territory that has taken years to achieve its natural balance . The whole system is shot to hell and you get -- say Candida , normally held in balance by the weaker micro organisms -- and there are many HARMFULL effects such as invasive candidiasis , etc.