Eleanor Acheson McCulloch Gamble

“ The anosmia of smokers cannot be wholly attributed to their catarrh, though a light, acute nicotine-poisoning does not seem to produce a loss of smell. Nervous anosmia may be congenital,—-i.e., due to imperfect development of the olfactory vesicle in the brain,—or may be senile,—due to degeneration of some of the nervous elements which condition the sense,—or may be due to exhaustion of the olfactory nerve, or to dryness of the epithelium. If we rule out exhaustion,we may say that respiratory anosmia is vastly more common than toxic or nervous. ”

“ Zwaardemaker of Utrecht has constructed an instrument which he calls an olfactometer. It consists simply of a glass tube, one end of which curves upward to be inserted into the nostril, A shorter movable cylinder made of the odoriferous substance fits over the straight end of this glass tube. In inhaling, no odor is perceived so long as the outer does not project beyond the inner tube. The farther we push forward the outer cylinder, the larger will be the scented surface presented to the inrushing column of air, and the stronger will be the odor perceived. ”

“ That heat and dampness affect the intensity of odors is a matter of common observation. Yellow wax smells twice as strong in summer as in winter. Heat promotes evaporation. Dampness also promotes the vaporization of such solids as are soluble in water, but, on the other hand, retards the diffusion of odorous vapors. The temperature of the laboratory in which smell experiments are in progress should be kept as uniform as possible, and thermometer and barometer readings should be taken whenever the stimulus-limen is determined. Uniformity of temperature was not secured in our own experiments. ”

“ With Rog, exhaustion often supervened in a long inspiration. If is clear that if the intensity of a stimulus alters with the duration of an inspiration as well as with the manipulation of the instrument, the subject must make more than one inspiration to determine a limen, unless the judgment is very easy, It is probable that the first part of the inspiration, before the smell “blossoms out,” gives the best criterion of the intensity of a stimulus. We would suggest that cumulative stimulation of smell would be a profitable subject of investigation. ”

“ However, it is at least possible that odors which have very different stimulus-limina should have the same difference-limina, The other method is that of exhaustion, and depends on the fact that different odors exhaust the organ with different degrees of rapidity, so that a compound odor, continuously smelled, will alter in quality as first one and then another of its constituents disappears. One may smell continuously the substance to be tested, or may smell it before and after smelling repeatedly an odor very similar in quality. ”

“ Zwaardemaker believes that each subject with a little practice will discover for himself the best rate of breathing for obtaining the strongest smell from a given stimulus, so that, in a manner, the breathing rate will be self-regulating. [70] Our own experimental results seem to bear out this conclusion. In Section 1 of Chapter III, each subject’s mode of breathing is noted, but its peculiarities can scarcely be traced in the numerical results. The inability of most of the subjects to arrive at difference-determinations with one inspiration must, of course, have aggravated the adhesion-error. ”

“ The influence of exhaustion is more insidious. It varies from subject to subject, from substance to substance, and from one intensity of a substance and one general condition of a subject to another, so that numerical corrections are out of the question. Fortunately or unfortunately, the effects of adhesion and exhaustion are for the most part opposite. This opposite influence makes one’s numerical results more nearly correct than they would otherwise be. On the other hand, it makes the exact influence of each source of error more difficult to read from the figures. ”

“ Strong smells hide the weak. [32] In view of the first objective difference, Zwaardemaker explains the subjective difference as follows : As the strength of a sensation is estimated by the number of grades of intensity by which it surpasses the liminal sensation, and as the terminal stimulus is by definition that degree of intensity beyond which increase cannot be shown for our human sense organs with our mechanical appliances, it is obvious that odors with large difference-limina must be subjectively weak, and that subjectively weak odors must have large difference-limina. ”

“ Under ordinary circumstances, as we have seen, the more rapidly one breathes, the stronger the odor one will get. If one uses the olfactometer, this is not true. Since the diffusion-rate within the cylinder is constant, increased rapidity of breathing will increase the degree in which the odorous particles are diluted with air on their entrance to the nasal passages. Thus, the more slowly one breathes, within a certain limit, the stronger the smell one will get. 'The air must be drawn in with enough force to carry part of the current above the lower turbinal bone. ”

“ Usually, the last movement made by the subject is an outward movement. He moves from a point decidedly different from the standard to subjective equality, and then a little way back again,—in and out once or oftener. In moving the cylinder the hand is apt to slip, and the accidental increment to Δr is a larger fraction of the smaller standard than of the larger. Adhesion is not a factor in the case, for it is larger for the larger standard, varies with the length of the determination, has an opposite effect upon Δro and Δru, and is balanced in an indefinite way by exhaustion. ”

“ The spaces from which air is drawn through the nose are cones with their points at the nostrils. We may see their size and shape in the clouds of vapor formed by our exhalations in cold weather, The spaces from which odorous particles are drawn are portions of these larger spaces. The breathing-spaces are projections of the whole of the nasal cavities ; the “fields of smell” are projections only of those cavities from which odorous particles reach the olfactory membrane. ”

“ Through the remaining cork of the second flask, which was filled only with air, was inserted a glass-inhaling tube which divided into a nose-piece for each nostril. The odor of the liquid was weakened by successive additions of water, and the intensity of the stimulus was measured through the proportion by weight which the ethereal oil bears to the water. [65] As Zwaardemaker suggests the method of Savelieff has this great disadvantage, that its results do not stand in simple relations to the real stimulus-intensities. ”

“ The tubes of soap, however, sometimes shrivel in a few days independently of the temperature. The longer the paraffine is heated the stronger the odor. Zwaardemaker succeeds in giving it an odor as strong as that of tallow or musk-root. We did not try beating it longer than an hour and a half, and our paraffine tubes gave the weakest of all our scents. Tubes of tallow are easy to make and to keep, and do not exhaust the subject's sense-organ to any appreciable extent, and are therefore especially to be recommended. ”

“ This is done that quantities of the other odorous substances large enough to allow for evaporation may be put into the solution without raising the intensity of the smell to the neighborhood of the terminal stimulus-intensity. [21] If, now, most smells are mixed, and if mixed smells alter in quality as the organ becomes fatigued, and if different olfactory qualities have not the same limina, then in quantitative work in smell, we are seeking to determine values which are continually changing according to laws which we do not know. ”

“ Respiratory anosmia is due to obstruction of the nasal passages, from asymmetry of the nasal skeleton, from hyperaemia of the respiratory or Schneiderian membrane, or from accumulation of mucus. Toxic anosmia may be due to poisons in the inspired air,—a form not yet investigated,—to injurious fluids introduced directly into the chamber containing the sense-epithelium (as in Aronsohn’s experiments) , to poisons, such as morphine, pulverized and blown into the nose, or to certain forms of blood-poisoning, such as chronic nicotine-poisoning. ”

“ Giving the subject a variable stimulus objectively equal to the standard, we bade him make it subjectively equal,—for it would tend to seem subjectively less from the effect of exhaustion,—and then after pausing to let us take the reading, to make it subjectively just greater than the standard, Then he was directed to make a variable stimulus very appreciably greater, just equal subjectively, Next, after making an objectively equal stimulus subjectively equal, he made it subjectively less, Lastly, he made an appreciably weaker stimulus subjectively equal to the standard. ”

“ We cannot satisfactorily explain the difference between our results and bis in the matter of stimulus-limina. That the limina of Americans should be higher than those of Dutchmen is not indeed surprising, but the entire change in the rank of the substances is. According to Dr. Reuter, as cited by Zwaardemaker, the gum ammoniac and gutta-percha cylinder is forty times es strong as the vulcanized rubber, and the musk-root is five times stronger than the former. The tallow, Zwaardemaker says, is stronger still. We regret that we could not find stimulus-limina oftener. ”

“ It is impossible, moreover, to take many determinations even of the stimulus-limen in an hour with a perfectly dry and clean tube. As for the difference-limen, it is both theoretically and practically impossible to make the adhesion-correction, for to know how much greater for sensation a given stimulus is than the liminal stimulus, one would have to know beforehamd that Weber's law applied to that particular olfactory quality, and what the exact value of Δr⁄r for the quality was. ”

“ By the indirect methods, he seeks to find the stimulus-limen in terms of the smallest quantity of the odorous substance which can be sensed under certain definite and easily procurable conditions. The direct methods aim at absolute results where absolute results are unattainable. “It may be possible,” says Zwaardemaker, “to determine the area of an inspiration made in an effort to smell, but the exact ascertainment of the amount of odorous gas which in this inspiration comes in contact with the olfactory cells has so far proved an impossibility.” ”

“ Zwaardemaker advises that the fluid-mantle of the porcelain cylinder be changed every two days. We usually not only changed the mantle, but made a fresh solution, as often as this. It is safe to use the same glycerine or paraffine solution for days or even some weeks. The glycerine is much more difficult to put into the receptacle than the parafiine, and for citral and caryophylline it is not so able a solvent. It is difficult, however, to obtain and keep liquid paraffine quite free from a slight odor, somewhat pungent and somewhat like that of vaseline. ”

“ The cylinder may be prepared by cutting 10 cm. from a rubber tube with a bore of 8 mm., and working it into a glass tube of the same length. The rubber must be clean and new, and, in particular, must never have come in contact with illuminating gas. Although the odor of the rubber when fresh is not easily disguised by other smells, yet the substance easily loses its own odor and takes that of other substances. An inhaling-tube or the broken fragment of one should, therefore, be left in the cylinder so as to cover its inner surface when not in use. ”

“ Odorous particles probably do not accumulate in the upper chamber. During inspiration, the air in the passages traversed by the current is thinned, and as soon as inspiration ceases, the air in the upper chamber rushes down to the middle meatus, to be renewed from the pharynx during expiration. [45] If so much odorous matter has been taken in as to saturate the air in the pharynx, we sometimes get a smell in expiration even when we are not eating. Ordinarily, however, the very weak stimulus from the pharynx, coming after the very strong stimulus from without, is not sensed. ”

“ The effect of adhesion, in the first inspiration or at least in the very first few inspirations, is to decrease the strength of the stimulus, but after the first or at most after the second or third inspiration, the effect is rather to increase the strength of the stimulus, since the odor from the matter adhering to the inhaling-tube more than compensates for the 1oss of the odor of the matter which continues to adhere. ”

“ The tubes with one curve are precisely like the inhaling-tubes of the standard olfactometer, except that the part which extends through the screen is longer and is not graduated. It is a mistake to use two-jointed tubes at all, unless both nostrils are to be used, as in compensation-experiments. The extra curve seems to make no difference in the results, but it makes the tubes much harder to clean. The total length of our two-jointed tubes was 18+1⁄2 cm., and that of our one-jointed tubes, 17+1⁄2 cm. 11.3 cm. of every tube used must project beyond the screen. ”