The Secret of Scent : Adventures in Perfume and the Science of Smell.
By Luca Turin
* Publisher: Faber and Faber / HarperCollins
* Number Of Pages: ix + 207
* Publication Date: 2006-05-18 (later in U.S.)
* ISBN-10 / ASIN: 0571215378 / 0061133833
* ISBN-13 / EAN: 9780571215379 / 9780061133831
From Booklist
Scientists who can poetically convey the worth of their research are rare individuals indeed. Many, in fact, migrate to the professional writer's life, such as Oliver Sacks and Michael Crichton. Turin, already the subject of a previous book (Chandler Burr's The Emperor of Scent, 2003), not only demystifies the "hows" of smell but also chronicles his own discoveries and pays generous homage to others'. Curious beauty noses will sniff out the origins of such famed fragrances as Chanel N5, Opium, and the ever-widening world of musks. ...
"Turin writes brilliantly, with the easy confidence of the expert and the infectious enthusiasm of the true amateur." -- Tim Radford, The Guardian
Miriam Solomon, in Science:
A delightful book about the science of smell, The Secret of Scent takes the reader through a tour of the almost infinite range of human olfactory possibilities. Luca Turin also presents the recent history of theories of smell, culminating with his own frequency theory. Turin possesses an unusually sensitive nose and has the ability to detect and describe, like a wine expert, the character of individual odors and complex scents, natural and synthetic, pleasing and noxious. A perfume guide he wrote became a best seller in France. The success of his perfume guide led to invitations to visit and consult with scent and perfume manufacturers, from which Turin learned much about the process of creation of scent.
In part because of this unusual access to perfumery materials and manufacture, Turin has found the leading theory of smell--that humans detect small volatile molecules by assessing the shape of the molecule or part of the molecule--unsatisfactory. Shape theories were originally proposed by Linus Pauling and R. W. Moncrieff in the 1940s and subsequently developed by John Amoore and others. Turin observes that research on creating new smell molecules is trial and error. Data mining for correlations between molecular shape and smell has not generated useful predictions. Scent manufacturers typically synthesize 1000 new molecules to get one that they can use. Turin observes that, contrary to the predictions of shape theories, molecules very different in shape can sometimes smell the same (e.g., boranes smell sulfurous) and molecules very similar in shape can smell different (e.g., isotopes of the same molecule such as acetophenone and deuterated acetophenone).
Turin has a Ph.D. in biophysics. At the time that he developed his theory of smell, he was a lecturer at University College London. His research has ranged from electrophysiology to protein semiconductors and work on solitons. He has always read widely in the fields related to his research.
The author knew of the theories of Malcolm Dyson (5) and Robert Wright (6), which claimed that smell (like sound and color perception) is based on frequency detection. For smell, the frequencies detected and measured are the vibrational frequencies of odorant molecules. Historically, the frequency theory faltered on the observation that enantiomers (mirror images of the same molecule, having the same vibrational spectrum) sometimes smell different and on the lack of a known mechanism for measuring vibrational frequency of molecules. Turin noted, however, that (as mentioned above) shape theories also have substantial contrary observations. He argues for a balanced look at all the evidence, and he considers the ability of each theory to accommodate contrary observations. Building on his earlier work on the electrical conductivity of proteins, Turin proposes that smell receptors are sensitive to particular ranges of vibrational frequency of molecules and use electron tunneling to transmit an electric signal when the appropriate odorant molecule is in the receptor. (This explanation is an interesting application of quantum mechanics to understand a physiological phenomenon.) Genomic sequencing by Linda Buck and her colleagues has identified about 350 different smell receptors in humans. Turin does not suggest that each smell receptor responds to a different range of frequency. He thinks it more likely that classes of smell receptors respond to the same ranges of frequency but fit different sizes and shapes of molecule. (In this way, Turin explains the findings about enantiomers, but also complicates his theory with a shape component governing the affinity of odorants for receptors.)
Journalist Chandler Burr's widely read and (mostly) favorably reviewed book (9) has already told the story of the development and reception of Turin's theory. Academic and commercial smell researchers alike have been largely dismissive of Turin's hypothesis.
The Secret of Scent is an interesting sequel, and partial corrective, to Burr's account. It is much more a book about science than about scientists, and it is refreshingly non-egotistical. Turin does not describe his own theory until page 160, and he presents the relevant contributions of many scientists from a range of scientific subdisciplines, including organic chemistry, the physics of electron tunneling, and the physiology of insect olfaction. Of particular note is Turin's coverage of findings from Soviet and Russian researchers.
Intended for a general audience, The Secret of Scent skillfully presents the necessary concepts from physics and chemistry. The book is not a polemic, but rather a straightforward presentation of odor, theories of odor, and the author's theory of odor in particular.
Turin continues to work with his theory, presently in a corporate rather than an academic context. He is currently the chief scientist of Flexitral, a privately held U.S. company that uses his theory to design new scents, seeking molecules that are cheap to synthesize and have favorable toxicological and environmental profiles. Turin claims a success rate of 10% (one in ten syntheses produces a commercially viable molecule), which is two orders of magnitude above the industry average. Perhaps he will persuade the corporate world to take his frequency theory seriously before the academic community does.
As one would expect, Turin wishes his theory had found a more positive reception. Insofar as he assigns blame for its current fate, he faults the process of peer review. Turin believes that in areas requiring a high degree of specialized knowledge, any competent referee will have a conflict of interest. Competition will get in the way of a fair review. Moreover, he thinks that interdisciplinary research is especially vulnerable to deficient review, because it is difficult to find reviewers with the required broad range of expertises.
The Secret of Scent should appeal to anyone curious about smell, whether as a researcher or an intrigued layperson. It also touches on various aspects of science practice and policy, including scientific creativity, the difficulties of interdisciplinary research, the importance of unusual skills, and the consequences of unusual access to data. And Turin's story will also attract those, like myself, interested in scientific controversy.
...in a more typical, negative review from Chemical Senses, vol. 33, p. 576:
"The mechanism of frequency analysis proposed by Turin—inelastic electron tunneling spectroscopy—is erroneous because free electrons have no natural occurrence in biology. Turin can be appreciated for his art of perfumery, but his 'science' of smell is contrary to facts and basic scientific principles." -- Thomas Hettinger.
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