VOICES OF EXPERIENCE 



seemed to make no sense, for the bats were completely 

 silent as far as anyone could tell, both before and after 

 they had been subjected to these various experimental 

 treatments. How could the ears replace the eyes in guid- 

 ing their flight? In 1800 there seemed to be no answer 

 to this question, and Spallanzani's findings were rejected, 

 ridiculed, and almost totally forgotten. Armchair critics 

 surmised that some refined sense of touch, probably 

 located on the wing membranes, accounted for bats' 

 ability to detect objects at a distance and thus avoid 

 them, but no one even tried to explain how Spallanzani's 

 four blinded bats had filled their stomachs with flying 

 insects. 



What came to be called "Spallanzani's bat problem" 

 was not solved until about twenty years ago after elec- 

 tronic apparatus had been developed at Harvard by the 

 physicist G. W. Pierce to detect sounds lying outside the 

 frequency range of human hearing. Just as soon as I 

 brought some bats to Pierce's apparatus, it became ob- 

 vious that they were emitting plenty of sound, but that 

 it was almost entirely above the frequencies that we 

 could hear. Further experiments, in collaboration with 

 Robert Galambos, now of the Walter Reed Army Insti- 

 tute of Research, showed that covering the mouth of 

 a bat and thus preventing its emission of these high- 

 frequency sounds was just as effective as plugging its 

 ears. Both treatments made bats quite unable to detect 

 large objects or small, and they bumped against the walls 

 of the room or anything else in their path. In short, 

 their whole orientation during flight depended upon 

 echoes of the high-frequency sounds that they emitted 

 almost continuously while flying about. Because these 

 sounds have shorter wave lengths, and consequently 

 higher frequencies, than those to which our ears respond, 

 the ability of bats to fly in total darkness had seemed 



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