Several prominent scientists of the time were interested in Spallanzani's results. One of them, Charles Jurine (1751-1819), had performed his own experiments. He discovered that he could ruin bat's ability to avoid obstacles in the dark by plugging their ears with wax

Spallanzani thought: perhaps Jurine's wax plugs distressed the bats, so it was no wonder they didn't fly too well. Spallanzani developed wax plugs into which he could insert specially made, tiny brass tubes. The tubes allowed sound into the ear canal. This way, he could compare bats with wax plugs in their ears who could hear, with bats with wax plugs in their ears who could not hear.