Notes on scientific research. 123 



8. These are the compounds exercising the sensation of odour on the olfactory 

 nerve which is then conducted to the brain. 



9. Hence, quite a series of conditions must be complied with in case that an odour 

 is to be rendered perceptible. If one of them is not answered to and there is 

 a missing link in the chain, no odour is noticeable. 



10. Odour is a chemical action on the sense of smelling. 



Tschirch speaks of the "solubility of the substance in air". In order to explain 

 this, scientifically incorrect, expression we add that the author refers to a paper 

 published by H. Erdmann 1 ) who inferred, from the easy solubility of aromatics in 

 liquid air, a specific solubility of there bodies also in gaseous air. For the sensation 

 of smell, not the volatility of the substance is deciding, but a different property which 

 Tschirch terms solubility in air. The author wishes to point out hereby that the 

 molecule of the aromatic, which emits a different odour when in concentrated and in 

 diluted state, undergoes changes due to the air. With increasing dilution a cleavage 

 down to the ions is expected to pass off, as in the case of aqueous solutions. 



F. B. Hofmann 2 ) has published a paper on the sense of smell basing principally 

 on self-observation. Owing to a severe catarrh of the nasal cavity the author had 

 nearly entirely lost his power of smelling, and but quite by degrees and very slowly 

 normal smelling sensation was recovered. During this period (several years), Hofmann 

 undertook systematically a large series of experiments, the result of which is as 

 follows: — 



In the beginning Hofmann was only able to perceive the odour of natural and of 

 artifical musk in their characteristic peculiarity and apparently also in their full strength. 

 Pyridine smelled strong, but not so unbearable as usually. Of other bodies, the author 

 had a sensation of odour with acetone and, quite indefinite as to character, of isobutyl 

 and isoamyl alcohols. When in the following weeks the sense for smelling pyridine 

 improved noticeably (the author made use of Zwaardemaker's olfactometer as modified 

 by Zimmermann), also other substances which hitherto were odourless for him became 

 noticeable. Ammonia and trimethylamine smelled strong; diethyl ketone, acetone, 

 amylene hydrate, ether, and chloroform somewhat less strong; butyl and amyl alcohols, 

 amyl acetate, butyrate, and valerate very weak, and thymol, toluene, and xylene 

 extremely weak. Only a trace of odour was noticed, inter alia, with benzaldehyde, 

 carvacrol, menthol, and phenol; yet Hofmann was able to differentiate between the 

 odour of these bodies. No odour whatsoever was perceptible with asa fcetida, iodoform, 

 mercaptane, scatole, and vanillin. 



Some months later Hofmann noticed that many of the substances mentioned 

 showed a strong smell, but quite different from their usual character. Normal behaviour 

 was exhibited, in addition to musk, only by vanillin. Indole remained quite odourless. 

 The author was particularly struck by the qualitative change in the different smelling 

 sensations after their reappearing. Violets and ionone, for instance, smelled in the 

 beginning like cigar tobacco, later on the true violet odour became perceptible. 



Even several years afterwards the author failed to perceive some special odour 

 characters. For him, putrefying albumen and scatole showed a faint sweetish odour, 

 sulphuretted hydrogen, carbon disulphide, garlic, and various spices, such as caraway, 

 an abnormal, indefinite smell. 



] ) Journ. f. prakt-. Chemie n. F. 61 (1900), 226. — 2 ) Zur Theorie des Geruehsinnes, I. Parosmie-Studien. 

 Zatgchr. f. Biologie 73 (1921), Nos. 1 to 4. As per a reprint kindly forwarded to us. 



