To the Editor: In their analysis of the energy expended in chewing gum
(Dec. 30 issue),1 Levine et al. instructed subjects to chew gum "at a
frequency of precisely 100 Hz (a value that approximates chewing
frequency at our institution) with the aid of a metronome." I am curious
about the use of hertz, the Système International unit of frequency
measured in cycles per second.2,3 As defined, a value of 1.0 Hz rather than
100 Hz would be more plausible. Alternatively, if the experimental
protocol had called for a setting of 100 on a standard metronome, as might
be inferred from the quoted text, the unit of measurement that should have
been used is Maelzel's metronome (MM), which indicates oscillations per
minute.4 A measurement of MM 100 is consistent with calculations based
on my own informal observations of gum chewing.
David A. Florman, J.D.
575 Madison Ave.
New York, NY 10022-2585
Dr. Levine replies:
To the Editor: Mr. Florman is correct: we did use erroneous units to describe the normal chewing rate at our institution. We should have used chews per minute rather than hertz. The rate of 100 chews per minute at our institution indeed approximates that calculated by Mr. Florman in New York City. The rate varies according to body size. In quadripeds, the chewing rate relates to body mass to the –0.128 power, a relation that relates primarily to jaw mechanics rather than to metabolic needs.1 Hence, larger organisms chew with greater thermal efficiency than smaller organisms, and I would not want to mislead readers of the Journal regarding any inefficiency at our institution.
James Levine, M.D., Ph.D.
Rochester, MN 55905