June 22, 1882] 



NA TURE 



187 



Wright. — On lacustrine concretions from Grand Lake, N.S., by 

 Prof. Honeyman, D.C L. — Illustrations of the fauna of the St. 

 John, N.B. group, by G. F. Matthew. — On buds fiom Hudson's 

 Bay, by Prof. Bel). — On a new classification of Crinoids, by 

 Prof. E. J. Chapman. This classification is based essentially on 

 the presence or absence of a canalicnlated structure in the 

 calyx and arm plates. Three leading divisions are thus recog- 

 nised. In one, the plates are without internal canals ; in the 

 second, the arm plates are perforated internally ; and in the 

 third, a system of canals radiates from the base of the calyx to 

 the extremities of the arms. The subdivisions have been worked 

 out to bring readily under grasp the more salient or broadly 

 distinctive features of all the better-known families and types ; 

 and as the common names of families embody very little indi- 

 cation of these features, an additional grouping into sections is 

 adopted. — On the Lower Cretaceous rocks of British Columbia, 

 by J. F. Whiteaves. — On the introduction and dissemination of 

 some noxious insects, by \Vm. Saunders. — On the geological 

 history of the St. John (N.B.) river valley, by Prof. L. W. 

 Bailly. — On recent discoveries in the life-history of Botrydium 

 granulatum, a terrestrial Canadian alga, as illustrating phases 

 of development in the lower forms of vegetation, by Prof. G. 

 Lawson, Ph.D., LL.D. — On the Quebec group of rocks, by 

 Dr. A. R. C. Selwyn. 



The following officers were elected : President, T. W. Dawson, 

 C.M.G., LL.D., F.R.S., Principal of McGill College, Mon- 

 treal ; Vice-President, Hon. P. J. O. Chauveau, LL.D. ; Hon. 

 Secretary, J. G. Bourinat, F.S.S., Ottawa; Hon. Treasurer, 

 J. A. Grant, M.D., Ottawa. 



ON SMELL 

 "THE sense of smell Is caused by the contact of certain sub- 

 ■*■ stances with the terminal organs of the olfactory nerves, 

 which are spread as a network over a mucous membrane lining 

 the upper part of the nasal cavity. Each nerve consists of a 

 number of small bundles, themselves capable of being split into 

 extremely fine nerve fibres. There are spindle-.- ha ped cells con- 

 nected « ith these nerves, from which proceed two [recesses — 

 one to the surface, provided with bundles of long hairlets ; the 

 other passes to the interior. It is these hairlets which are pro- 

 probably the proximate cause of smell. 



Let us consider, first, by what are smells excited? The 

 operation of smelling is performed by sniffing, that is, by a 

 series of short inhalations of air, bearing with it the odorous 

 body. The first question which suggests itself is : Is the sub- 

 stance which excites sensation a liquid, solid, or gas ? It has 

 been tried by Weber, to fill the nose with eau-de-Cologne and 

 water, lying on the back for that purpose, and pouring ihe liquid 

 into the nostrils by a funnel. No sensation is produced. I 

 have myself tried the experiment, and can confirm his observa- 

 tion. There is an irritating feeling, but no smell. Of course, 

 on washing out the nose, or blowing it, the characteristic smell 

 is at once noticeable. 



It is easy to prove that solid particles are not the cause of 

 smell. If the air conveying the odour be filtered through a tube 

 filled with cotton wool, and insetted into the nose, a smell is 

 still discernible, although all solid particles must thereby be kept 

 back. But it is a very remarkable circumstance that it is so, for 

 one would not suspect such extremely non-volatile substances as 

 copper, iron, silver, &c, to give off gas, if indeed the smell 

 which they most certainly evolve when mbbed is due to the gas 

 of the substance. 



We must, therefore, conclude that the sense of smell is ex- 

 cited by gases only. It is of course necessary to include under 

 the name gases the vapours of liquids or solids which have low 

 vapour-tension, and which, in consequence, give off vapour at 

 the ordinary temperature. It has been proved that this is the 

 case even with mercury, the boiling point of which is over 300° 

 Centigrade. We may con-equently conclude that many other 

 substances of which it is impossible to measure the vapour-ten- 

 sion at ordinary temperatures, owing to its extreme minuteness, 

 also evolve gas, if only in very small quantities. But it is 

 well known that all gases have not the power of exciting a sense 

 of smell. Let us compare some gases which have smell, with 

 some which have none, and endeavour to discover if those which 

 have smell have any other property in common. 



The following is a list of gases which have no smell .—Hydro- 

 gen, oxygen, nitrogen, water-gas, marsh-gas, defiant -gas, carbon 

 monoxide, hydrochloric acid, formic acid vapour, nitrous oxide, 



and ammonia. Those which possess smell are chlorine, bromine, 

 iodine ; the compounds of the first two with oxygen and water, 

 the second three oxides of nitrogen (or perhaps it is right to say 

 nitric peroxide, for the other lower oxides are changed into it 

 when they come into contact with air) ; the vapours of phosphorus 

 and sulphur ; arsenic and antimony ; sulphurous acid, carbonic 

 acid, and almost all the volatile compounds of carbon, save those 

 already mentioned ; some compounds of selenium and tellurium ; 

 the compounds of chlorine, bromine, and iodine, with the above- 

 named elements ; and some meials. 



In considering this list, I submit first, that the property of 

 smell is peculiar to some elements and their compounds. Thus, 

 chlorine, bromine, iodine, sulphur, selenium, and tellurium, 

 which are volatile or give off vapour at ordinary temperatures, 

 have a characteristic smell. We should expect their compounds 

 to have a smell, and we find this to be the case. Second, those 

 substances which have no smell, or produce simple irritation of 

 the nostrils have all low molecular weight. Such is the case 

 with hydrogen, the element of lowest specific gravity. Such 

 also is the case with oxygen and nitrogen ; but this as well as the 

 absence of smell in water- vapour, may be ascribed to the constant 

 presence of these gases in our atmosphere, and their necessary 

 constant presence in our nostrils, so that we may be insensible to 

 their smells because we are always inhaling them ; but I think 

 it probable that this is not so. Hydrochloric, hydrobromic, and 

 hydriodic acids, and ammonia, have purely an irritating effect, 

 and cannot be described as smells. When ammonia is pure and 

 free from compounds containing carbon, it has no trace of smell. 

 Nitrous oxide is also the lowest of the oxides of nitrogen, and as 

 such has the Iowe.-t specific gravity. But it is when we turn to 

 compounds of carbon that we are best able to draw general con- 

 clusions ; for that element, far excellence, has the faculty of 

 forming almost innumerable compounds, and series which 

 resemble each other in properties, but differ in specific gravity. 

 And here we are most struck with the fact that increase of mole- 

 cular weight, i.e. increase of specific gravity in the form of gas, 

 produces, to a certain point, smell. Let us examine the simplest 

 series, viz. the marsh-gas or methane series, commonly called the 

 paraffins. The first two of these have no smell. Ethane, indeed, 

 which is fifteen times as heavy as hydrogen, begins to have a 

 faint trace, but it is not till we arrive at butane, which is thirty 

 times heavier than hydrogen, that a distinct sensation of smell is 

 noticed. In the same manner, the olefine series, of which the 

 first member is ethene, or olefiant gas, gains in smell with rise 

 of molecular weight. Of course, the highest members of this 

 series have no smell, for they are non-volatile, but this is the 

 case with most carbon compounds of which the molecular 

 weight is high. 



A similar relation is noticeable among the alcohols. Methyl 

 alcohol, in a state of purity, is smell-less ; ethyl, or ordinary 

 alcohol, when freed from ethers and as much as possible from 

 water, has a faint smell, and the odour rapidly becomes marked 

 as we rise in series, till the limit of volatility is reached, and we 

 arrive at solids with such a low vapour tension that they give off 

 no appreciable amount of vapour at the ordinary temperature. 

 Again, with the acids, formic acid is smell-less, and produces a 

 pure sensation of irritation. Acetic acid has a slight but charac, 

 teristic smell ; and the higher acids of the series, propionic 

 butyric, valerianic acid, &c, gain in odour with increase in 

 density in the form of gas. If we consider the nitrogenous 

 compounds of carbon, we are led to the same conclusion. Prussic 

 acid is not smelt by more than four persons out of every five ; 

 but the nitriles, which bear the same relation to prussic acid as 

 the higher members of a series bear to the lower, have all very 

 characteristic odours. Acetylene would appear to form an ex- 

 ception to this rule ; but carefully purified acetylene has little 

 odour, and it is surpassed by its higher homologues. We may 

 therefore, I think, accept this as a principle— that the intensity 

 of the smell rises v. ith rise in molecular weight. 



It is also noticeable that the character of a smell is a property 

 of the element or group which enters into the body, producing 

 the smell, and tends to make it generic. Thus we can charac- 

 terise the compounds of chlorine and its oxides as chlorous ; 

 indeed we may group the three elements — chlorine, bromine, and 

 iodine, together, and name the characteristic odour of them and 

 their oxides haloid smells. Similarly, sulphur, selenium, and 

 tellurium, in their compounds with hydrogen, have a generic 

 smell ; and likewise arsenic and antimony. The only oxide of 

 nitrogen which is smelt is nitric peroxide, so that it is impossible 

 to pronounce on a generic smell for this substance. It is, again, 



