But I will take an example from the practice of physicians, as well as from quackery. The stimulating practice, of which some have been so fond as to apply it quite extensively in the treatment of disease, furnishes a good illustration of my remarks. As a system it is bad, just as a system on the opposite extreme is bad. And yet either of these systems is good in some cases, and often both are applicable to the same case in different stages of it. The truth is, that no _exclusive_ system of practice can be said to be a good system, for it is impossible that it should suit all the varying states presented by disease.[25] It is now sufficiently obvious to the reader, that I mean by bad practice, simply that which is inappropriate to the particular case under treatment. And it is also obvious to him, that a correct decision upon this point, made from observation of results, is arrived at with much more difficulty, than it would be, if what is good in practice were wholly and always good, and what is bad were wholly and always bad. I will now proceed to show what are the real points of difference between the results of good, and those of bad practice, and why it is that the community are so liable to mistake in their attempts at comparing these results. In the chapter on the Uncertainty of Medicine, I treated quite at large of the _vis medicatrix naturæ_, or the tendency of the system to throw off disease, and thus cure itself. _In the great majority of cases of sickness which fall under the care of the physician, this recuperative power is competent to effect a cure if they are left to themselves, and in most of them it will do so, even though a positively bad treatment may be pursued._ Let me not be understood to say that the kind of treatment which these cases receive makes no difference with them. It does make a great difference; but this difference does not ordinarily have any direct and present relation to the question of life and death, but it lies in circumstances which may be subjects of dispute, viz., the length of the sickness, the course which the symptoms take, the injury inflicted upon this or that organ, or upon the constitution, &c. Of these points I shall soon speak more particularly.