ECHOES OF BATS AND MEN 



ing from a night of active flight and food gathering. Like 

 all bats that are found in temperate cUmates, these fed 

 exclusively on insects, flying insects which they had to 

 pursue and catch on the wing. Spallanzani caught four 

 of the bats he had blinded a few days earher, and on 

 dissecting them found that their stomachs were just as 

 tightly crammed with the remains of insects as the other 

 bats, which had not been bUnded. 



Spallanzani performed a number of other experi- 

 ments, which, together with those of the Swiss biologist 

 Charles Jurine, led him to conclude before his death in 

 1799 that, while bats could dispense with their eyes, any 

 serious impairment of their hearing was disastrous. 

 When their ears were plugged, they coUided blindly and 

 at randdta with whatever obstacles were set in their way. 

 Only a really tight closure of the ear canals sufi&ced to 

 produce total disorientation, but Spallanzani's experi- 

 ments were completely convincing. One example of the 

 ingenuity of his methods was the way he investigated the 

 possibility that the bats' navigation might be disturbed 

 by irritation or injury caused by the earplugs rather than 

 by interference with hearing. He had some tiny brass 

 tubes constructed and fitted them into the ear openings 

 of the bats. This was no easy job in the 1790s since bats' 

 ear canals are less than one millimeter in diameter. When 

 the tubes were in place but open, the bats could still fly 

 with almost normal skill. When the same tubes were 

 tightly plugged, they caused no greater irritation, yet the 

 bats were now wholly disoriented and bumped at ran- 

 dom into every obstacle. No matter which of several 

 methods he used to close the ear openings, if the closure 

 was a tight one, the bat was helpless. 



On the other hand, a wide variety of other experi- 

 ments disclosed no effect of impairment of other sense 

 organs— vision, touch, smell, or taste. But these findings 



28 



