as far in as possible. It apparently proceeds from such space as there is between the inside surface and the inhaling-tube. The inhaling-tube, on the other hand, must not fit too closely in the inside of the odorous tube, for if it does, the subject will be able to move it only in irregular jerks, and it will, moreover, scrape off shavings from the inside surface of a cylinder of soft material, such as asafœtida or oil of mace. When it is used with the Russian leather, a bit of paper may be gummed around it to make it fit somewhat more closely. Even this, however, does not keep the smell of the leather from making itself apparent in the space from which one breathes through the tube. We attempted to find “negative stimulus-limina” for the troublesome substances, in the following manner: We used a graduated inhaling-tube 4 cm. longer than the ordinary one, and adjusting the cylinder over the 10 cm. nearest the screen, moved out to fignd the limen. The device was not successful. The odor still diffused itself through the space from which the air was drawn. All the determinations of difference-limina for these substances involve a constant error,—namely, the addition of an increment, which we have no means of measuring, to every stimulus represented on the tube.
II. Preparation of Odorous Substances in Solution. Of the odorous substances used in solution, the caryophylline, citral, vanilline, coumarine and heliotropine were among the “De Laire Specialties,” and were, with the ethyl butyrate, tincture of musk, and oil of camphor, the gift of Messrs. Dodge and Olcott, of New York. “The De Laire products,” writes a representative of Dodge and Olcott, “are not an embodiment of the simple chemical formulas suggested by their names. They are compounds after secret recipes, and their names denote only the odor or flavor or other quality which it is claimed they reproduce or imitate. De Laire's caryophylline, for example, is not the caryophylline of your chemical formulas, a distinctly solated aromatic principle, but a preparation, baying doubtless as its base one of the clove-oil products, which is intended to supply the perfumer with the bouquet of the clove-pink.” We have retained the De Laire spelling of their own specialties. The chemical formulæ of butyric ether, valerianic acid, allyl sulphide, and pyridin are, respectively, C3 H5 C4 H7 O2, C5 H10 O2, (C3 5 S, and C5 H5 N. The butyric ether used was a commercial product, but the valerianic acid was obtained at the chemical laboratory of the University, and the allyl sulphide and pyridin, as well as the oil of anise, were had of the Theodore Metcalf Company, of Boston.
Our solvents, mixtures, and concentrations were as follows:
| Oil of camphor in liquid paraffine, a mixture, | 1:500 |
| Caryophylline in pure glycerine, a true solution, | 1:500 |
| 0il of anise in liquid paraffine, a mixtnre, | 1:1663⁄4 |
| Valerianic acid, in water, a true solution, | 1:1500 |
| Ethyl butyrate,“““ | 1:1000 |
| Citral, in liquid paraffine,““ | 1:500 |
| Vanilline, in pure glycerine,““ | 1:125 |
| Coumarine, in liquid paraffine,““ | 1:1000 |
| Heliotropine, in liquid paraffine,““ | 1:125 |
| Natural Musk, the ordinary alcoholic tincture, in water, a mixture | 1:125 |
| Allyl Sulphide, in liquid paraffine, a true solution, | 1:1000 |
| Pyridin, in water, a true solution, | 1:500 |
| Laudanum, the ordinary alcoholic tincture, a true solution, unmixed. |
Some of the musk was of course precipitated by the addition of so much water, and floated about in dark brown specks, a state of affairs anything but desirable.
