Final answer:
Iodine antiseptic is used to clean a cerebral spinal specimen spill to prevent infection from bacteria.
Step-by-step explanation:
The substance used to clean a cerebral spinal specimen spill is iodine antiseptic. It is used to swab the lower back before performing a spinal tap, which is a procedure to collect cerebrospinal fluid (CSF) for analysis. The iodine antiseptic helps to prevent infection from bacteria that may be present on the skin.