If the operation of stimulant substances be closely observed, it will be noticed that, while some are slow, moderate, and lasting, others are, on the contrary, quick, energetic, and proportionably brief in their action; though the two sets run together by almost insensible gradations. This difference of operation was made by Dr. Murray, of Edinburgh, the basis of a division of the general stimulants into two distinct sets, which he named respectively permanent and diffusible stimulants. Though these terms are neither of them very accurately expressive of the distinctive characters of the two divisions, yet it may not be easy to find better, and it is advisable not to adopt new names unless upon some real ground of preference. I have, therefore, admitted this division with the nomenclature.