Much knowledge has already been gained regarding the nature of light and sound, and much is known as to the functions of both the eye and the ear. Little, however, has been learnt concerning the production of smell and taste, which is not the intellectual property of every educated man. The views of Hobbes and Hartley have been during late years rendered more acceptable by the remarkable discovery that the end-organs of special senses are all built up on the same plan. Developed as they are on the same lines from simpler, practically identical, ectodermic cells, we are forced with Herbert Spencer to look for similarities in the agencies which develop them. In the case of sight and hearing, it is already known that the quality of the sensation produced depends upon the nature—rapidity, complexity—of the vibrating stimulus. The particles of a liquid, as well as particles dissolved in water, are in constant and characteristic vibration. It has been my endeavour to discover whether in the case of taste also it will not be possible to connect the quality of the sensation with the nature or character of the vibration of the sapid particle.