I cannot go on with the multitudinous illustrations of these principles. The law is to determine injurious influences to the surface. Deposition in the cellular tissue of the lung is bad enough; but it is better—that is, less certainly fatal—there, than in the respiratory tubes: and that is the explanation. But now comes the practical point. How is the primary organ to be got at? because that is the way to carry out the removal of the impediments to the sanative processes of nature, which, in many cases, no _mere general_ treatment can accomplish. This is to be found by an examination into the _whole_ (that is, the former _as well as_ the more recent) history of the case, and adding the further test of a real and careful observation of all the secretions. By going back to the former life of the patient, we shall seldom fail to discover the various influences to which he has been subjected, and the organs to which they have been originally addressed. Having made up our minds, from our previous knowledge of injurious influences, on what organ they will most probably have acted, we now test this, not merely by inquiry after symptoms—and it may be not by symptoms at all—but by careful observation of the _actual work_ of the suspected organ. In this way we almost certainly discover the real offender; in other words, the organ primarily affected. This is of immense importance; for we confidently affirm that _one single beneficial impression made on it_ will do more in a short time—nay, in some rare instances, _in a single day_—than years of routine treatment, that has been, nevertheless, of good _general_ tendency. In treating it—_i. e._ the primary organ—however, great discrimination is necessary. If it be already organically affected, that treatment which would be, under _other circumstances_, necessary, becomes either objectionable, or requiring the utmost caution. For although an organ _diseased in structure_ will, under some circumstances, as Abernethy long ago observed, yield its characteristic secretion, yet, unless we know the _extent_ of the disease, which is just the thing we can almost never be certain about, excitement of it is _never without danger_. We should therefore excite the primary organ with more or less energy, with more or less caution, or _not at all_, according to circumstances. If we determine on not exciting it, we should then act on organs _with_ which it has ordinarily closest _community_ of function, or on whose integrity we can most depend. For choice, we prefer organs which, in a natural state, have nearest identity of function, as having the readiest sympathy, it may be, with each other. Yet so universal is the sympathy between all the organs, that there is no one that will not, under certain circumstances, or which may not be induced, perhaps, by judicious management, to take on _compensating_ actions.