Page:Eleanor Gamble - The Applicability of Weber's Law to Smell.pdf/23

Rh Ottolenghi used 12 aqueous solutions of essence of cloves contained in similar bottles in similar quantities. The solutions were graduated from 1:50000 to 1:100. The subject began with the weakest solution and took the bottles successively until sensation commenced. Pasay dissolved a certain weight of odorous material in a given weight of alcohol, mingled a certain fraction of the solution with a given weight of pure alcohol, and 80 on, until he had obtained a graduated series of saturations. He then put single drops of his solutions into bottles of the same size, and arrived by the method of just noticeable stimuli at an estimate of the stimulus-limen in terms of saturation-strength and the area of his bottles. Ottalenghi’s combinations of essence of cloves and water were not true solutions. Passy’s results are vitiated by the compensating effect of the odor of the alcohol. Both methods involve an error due to the constant loss of odorous material by the mere opening of the vessels for the subject to smell their contents, by inhalation, and by condensation on the walls of the vessels. Zwaardemaker suggests that fairly satisfactory results might be obtained on Ottalenghi’s principle it one (1) employed only solutions in distilled water, (2) made very short inspirations, (3) used very large inhaling vessels, and (4) avoided all odorous substances the vapor of which is easily condensed. Theoretically, if the series of saturation could be minutely enough graduated, this method might be employed for difference-determinations, but practically, the use of many large inhaling-vessels would make it too clumsy.

The first indirect method was invented by Frölich in 1851, three years after Valentin invented his direct method. Frölich ganged the keenness of smell by the distances at which odorous substances could be sensed under uniform conditions. He put up in tightly corked test-tubes such substances as ethereal oils, resins, spices, and musk mixed with starch in such proportions that however different in quality, the odors might be the same in intensity. The subject closed his eyes, the tube was uncorked and moved toward him, and both the distance at which the substance was first sensed and the time at which judgment was passed were marked. Frölich seems, however, to have made little use of his time-estimates. As the odors with which he worked are slowly diffused, the mass of odorous vapor may be thought of as moving with the tube, yet results based on such a rough hypothesis cannot be very reliable. Moreover, the assumption that odors so unlike in quality are of the same intensity, since they can be just sensed by the same person at the same distance, begs the question of the value of the hypothesis mentioned, and Frölich seems to have had no other means of determining their comparative intensity except guess-work.

Aronsohn’s famous method, devised in 1886, though indirect upon the ordinary theory of smell which makes the odorous particles act in gaseous form on the olfactory membrane, must be classed on Aronsohn’s own premises as direct. His hypothesis is that odorous particles are in solution when hey act on the nerve-endings. This assumption, for which J. Muller is chiefly responsible, is based (1) on the fact that fishes and amphibia have peripheral and central organs similar to the organs of smell in birds and mammals, and (2) on the fact that the nasal membranes are normally covered with mucus,