seconds with the standard olfactometer, and 5 seconds with the fluid-mantle olfactometer. With the small olfactometer, it was never less than 2, and almost never greater than 4 seconds. It was ordinarily 2. With the large olfactometer, it varied from 4 to 6 seconds. The difficulty in manipulating the large olfactometer more quickly will be described in another place. The interval between determinations was much more variable. It was usually about a minute, except when the tube was cleaned. Our determinations were broken into short series in which Δro and Δru were found alternately, The series were divided from each other by the necessary cleanings of the inhaling-tube. With some substances, we washed and dried the tube after every 8 determinations, wiping it out with dry absorbent cotton in the middle of the series. With other substances, we washed and dried it at the end of every 4 determinations. It took about a minute to give the tube a dry wipe, making the interval between half series about 2 minutes. After practice, it took about 3 minutes to wash, wipe and dry the tube, making the interval between series about 4 minutes, These time estimates are all rough. We were not intent on time-determinations; the subject had often incidental remarks to make on his own experiences; and there were various untoward accidents,—water spilled, tubes broken, wire dropped, etc. The subject used his two nostrils alternately ; all our records were kept for the two nostrils of each subject as for two different persons. We changed the order of determinations in successive series that exhaustion and adhesion might equally affect Δro and Δru for the right nostril and for the left, For example, 4 series might run thus:
(1) Δro f. R. N., Δro f. L. N., Δru f. R. N., Δru f. L. N.
(2) Δru f. L. N., Δru f. R. N., Δro f. L. N., Δro f. R. N.
(3) Δru f. R. N., Δru f. L. N., Δro f. R. N., Δro f. L. N.
(4) Δro f. L. N., Δro f, R. N., Δru f. L. N., Δru f. R. N.
With the standard olfactometer, after some practice in cleaning the tube, we took usually 32 determinations in an hour ; with the fluid-mantle olfactometer, 24. It was not worth while to take more even if there was time, as the effect of exhaustion became too marked. Fortunately, the odors of the solids used with the small and easily handled olfactometer, were less exhausting than the insistent smells of most of the solutions.
With an unpracticed subject, we used one standard a day. With a practiced subject, we took determinations first with a weaker, then with a stronger standard on the same day, If the substance was very exhausting, we worked first with a weaker, then with a stronger, then with a weaker, then with a
