able to tell us whether or not there is any relationship or correspondence between odour and chemical constitution.
When investigation of this point was begun, a hopeful fact came to light, as it was pointed out that certain bodies of similar chemical composition had all the same kind of smell. These were the compounds of arsenic, bismuth, and phosphorus, all of which smell of garlic. But it was soon realised that this fact was of little or no significance, as the oxides of many of the metals, although quite different from the former group, also smell of garlic. To these we may add the instance of water and sulphuretted hydrogen, two substances which are related chemically, as their formule show (H2O and H2S), and yet one of them is odourless, while the other has a strong, unpleasant smell. Finally, according to Deite, natural and artificial musk have nothing in common but their smell. Chemically they are quite different.
The property of odour, then, does not depend upon the chemical constitution of bodies.
The next question that arises is : Do bodies exhaling the 8ame kind of odour resemble each other in the structure of their molecules ? In other words, can odour be related to molecular structure ?
To the chemist all matter is made up of atoms and molecules. The elements, bodies which can-
