We may also sometimes discover specific action by the sensation of which the action is productive. Thus, for instance, cancer produces a burning kind of pain, which never attends simple ulceration. Specific ulceration is also always surrounded with more or less simple inflammation, or erysipelas, of the surrounding skin. In some cases the margin is hard, in others ragged, &c. It were much to be wished, that some more certain, and less arbitrary criteria, than those which we possess of the presence of specific action could be discovered; but, as yet, we know of no other which can be applied universally. Some kinds, indeed, are so well marked, and so peculiarly distinguished from simple sores, that they can be tolerably well described, and easily discovered to be specific; but, there are others which it is more difficult to ascertain, owing to the difficulty of fixing the character of each individual action. The number of specific inflammations is very great, and the causes which produce them are often obscure. In the preliminary dissertation it was mentioned, that, whenever any action existed strongly in any one part, it tended to induce an inflammatory state. There are, therefore, no general, or febrile diseases, which may not be attended with peculiar inflammations. That typhus fever is attended with local inflammatory action is pretty certain; but the presence of specific inflammation is still more evidently seen in the different exanthematous diseases. The diseases called cutaneous, afford us also numerous instances of specific inflammation. From the difficulty of discriminating betwixt diseases, which, although essentially different from each other, yet possess a very great similarity, we find, that the number of specific inflammations is confined much within the true limits; for we find many confounded under the name of herpetic, &c. which are radically different from each other. Phagedena has been used by medical writers in a very extensive sense, and has been made to comprehend diseases, which, strictly speaking, cannot be considered phagedenic.