Page:Eleanor Gamble - The Applicability of Weber's Law to Smell.pdf/21

Rh 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. They are separated from each other by about a centimeter. In sniffing, through the expansion of the nostrils, the fields of smell become wider than the ordinary breathing-spaces, but as the inspiration is short and quick, they are not so deep.

If then the strength of a smell-stimnlus is to be measured with some degree of accuracy by the genetic unit, the temperature and moisture of the air, the diffusion-rate of the vapor, and the subject’s manner and rate of breathing must be kept as uniform as possible.

As for the compensation-error, there is no intrinsic stimulation of the olfactory membrane as there is of the retina and the ear. Owing to exhaustion, the subject cannot smell his own breath in expiration. He can indeed smell it in inspiration if the current is puffed upward to the nostrils. This fact seems to show that, given the same amount of odorous matter in the air current, we get a stronger smell in inspiration than in expiration. On the other hand, the difficulty of securing an absence of smells from external sources for a subject who has at all cultivated his organ by attention, transcends the difficulty of securing such silences and darknesses as are satisfactory for experimental purposes. Of course, no substance which, as such, is to be used as a test, should be dissolved in an odorous medium, such as alcohol, ammonia, or ether.

Zwaardemaker classes the methods which have so far been employed to find the stimulus-limina of smells as direct and indirect. By the direct methods the subject seeks to find the stimnlus-limen of an olfactory quality in terms of the greatest dilution of an odorous vapor which can give a just noticeable sensation of that quality. 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.” The indirect methods aim at relative results, but their procedure is exact. They furnish a