I need not dwell longer upon the proofs of the fact, that the comparative success of different physicians, and different modes of practice, is not easily discovered by the public, nor even always by the scientific observer. Before I proceed to show why such a difficulty exists in regard to this point, it is best that the reader should understand distinctly what I mean by good and bad practice. I do not mean by good practice, the use of remedies which are essentially good, that is, beneficial in all cases; nor by bad practice, the use of remedies which are essentially bad, that is, injurious in all cases. There are no such medicines. Thompsonians claim that there are—that cayenne, lobelia, &c., are always beneficial, while calomel, opium. &c., are always deleterious. And this view of the subject is not confined to Thompsonians. There is a strong tendency to this exclusive notion in regard to remedies and systems of practice abroad in the community, and it is occasionally witnessed even in members of the medical profession. If it were true, that some one system of remedies and doctrines is wholly good, while all others are bad, it would be very easy for the community to decide between what is good, and what is bad practice in medicine. It would only have to watch, and whatever it saw uniformly doing harm reject, and whatever it saw uniformly doing good retain. But the subject is not thus simplified. There are some good points in every system of practice. However bad it may be on the whole, it will do some good in some cases. For example, the Thompsonian system, though it is bad as a system, inasmuch as it is injurious, often destructive in its results as applied indiscriminately to all cases, yet sometimes does good, and very often in the same case does at one stage of it good, and at another harm. Thus an attack of fever, especially if it depend upon a disordered stomach, may be broken up by an emetic of lobelia. Though commonly some other emetic would do it better, yet there is no question that in such a case the lobelia ordinarily does well. Now, after this is done, if the case were left to itself with rest and a simple diet, the cure would soon be completed. But the Thompsonian often undoes in part, and sometimes wholly, the good which he has done. By his heating remedies he induces a slight fever, with a morbid state of the mucous membrane of the stomach, indicated by a bad tongue, red, or furred, or both; and he thus makes a lingering case of one which should have been a short one, and perhaps creates slow disease, of which the patient may never get rid by any treatment.