We are aware that all the concentrations are startlingly high. We could not, however, use lower concentrations if we were to fix our standard-stimulus in two places on the scale. With a few exceptions, our stimulus-limina were much higher than those given by Zwaardemaker as normal, These facts will be noted later in detail. Zwaardemaker recommended vanilline in glycerine in the concentration of 1:7000 and coumarine and allyl sulphide in paraffine in the same concentration as especially well fitted for difference-determinations. We did use the coumarine and allyl sulphide in these concentrations, but most of our subjects obtained no odor whatever from the vanilline at 1:1000, and in no case did the stimulus-limen fall for both nostrils below 36 mm.
For coumarine, heliotropine and tincture of musk, stimulus-limina were found in a satisfactory manner. With all the other substances, an odor was apparent when the pointer of the fluid-mantle olfactometer stood at zero. The odor, undoubtededly, came from the space between the inbaling-tube and the inside of the porcelain cylinder, as great pains had been taken to wash away every drop of liquid from the metal plates. It is almost impossible so to adjust the inhaling-tube that it will not scrape against the clay at some point, and to paste paper around it would be out of the question, since the paper would continually rub and wipe the odorous surface. The odor was apparent 4 cm. from the end of the ordinary inhaling-tube when the cylinder was supposed to be sealed. All the determinations of difference-limina for these substances also are, therefore, subject to a constant error, but not so great an error as occurs in the results for the troublesome solids with the exception of Russian leather. The odor of the solutions when the instrument was closed was usually barely liminal.
When water was used as a solvent, it was, of course, distilled. The measuring-glasses and the bottles used should be rinsed well with distilled water, or at least with water which has been freshly sterilized by boiling just before the liquids are poured into them, An aqueous solution becomes unfit for use if long exposed to the light. 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. Alcoholic solutions are, of course, more or less undesirable, as we have noted before. If Δr⁄r were known to be the same for all qualities, there would be no objection to using such solutions, but to assume that it is, is to beg one question at issue. We could not manage the musk and the opium, however, in any other form.
Section 3. Other Arrangements and Appliances.
For cleaning the inhaling-tubes, one needs a funnel of which one end is small enough to fit into the bore ; two small light vessels,—tin cups are best,—for pouring water back and forth through them ; a roll of absorbent cotton ; a piece of pliable brass wire ; some listerine ; and a small alcohol lamp. After a tube is washed, it must be wiped inside and out with absorbent cotton before it is dried more thoroughly over the spirit-flame, else it will break. We used listerine occasion-
