Δr⁄r=1⁄4 in both cases, then Δr will be 6 in one case and 11 in the other, and we must write the values of Δr⁄r 24⁄80 and 22⁄80.
We believe that (3) a fortuitous circumstance in connection with the standard olfactometer is another factor in the same result. 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.
It should be noted in Table II that at first Δru is usually slightly larger than Δro, but that with practice this variation is reversed. The natural effect of exhaustion is to make Δro larger than Δru, for exhaustion does not affect the standard stimulus and stimulus of comparison equally, but progresses all the time that the latter is manipulated. This tendency is in a manner checked by the time-error and by adhesion, (See Chapter I, Section 4.) Now Be., the one subject who had had some experience in smell-experiments before the beginning of this course, tended from the first to make Δro greater than Δru. All the other subjects at first made Az greater than Avo, but all except Rog., Se. and Sk. changed the tendency with practice or began to do so. Rob.', N. and T. altered it very soon and decidedly. With Se. the values were usually almost equal, This alteration with practice seems to show that exhaustion causes more disturbance than adhesion and the time-error put together, This is what we should expect, for although the subject rested while the tube was being cleaned, yet the removal of adhesion was absolute,while the recuperation of the organ was less complete each time.<ref>Zwaardemaker : op. cit., pp. 203–204.<ref> We never can be quite sure, however, whether exhaustion is really decreasing the strength of stimuli regularly, or is blunting all differences or making all movements haphazard. When a subject complained that bis nose felt “hot,” “dry,” “rough,” “scrapy,” “sore,” or “numb,” his movements were often erratic, and the smaller stimulus sometimes seemed as strong as the larger, which probably stunned the already weary organ instantly. The dryness, no doubt, was due to the vigorous breathing. The tongue of a fever-patient will become much more parched and black if respiration through the nose is obstructed.
The original tendency to make Δro decidedly smaller than Δru, and the difficulty of finding the lower stimulus-limen are probably due to the same cause. Both cumulative stimulation and memory after- images might produce the tendency, though both would be counter-acted in a measure by the moving to and fro at the limen. Against both, the subject would learn to guard in a measure, Be. mentioned “after-images” of cocoa-butter, and Se. of tolu balsam. Frequently a subject would complain that he could not “get the strong smell out of his nose.”
