In _all_ these cases there has been activity of the vessels of the eye, and in all it has been relieved by secretion. Now this is the universal mode throughout the body; all irritation of the organs is attended by secretion; and where this is done, there is no disorder; or rather, the disorder is relieved: but if organs are irritated _continuously_, another thing happens, and that is, that an organ becomes unable to secrete constantly more than is natural, and then _some other_ organ, less irritated in the commencement, takes on an additional duty—that is, the duty of the animal economy is _still done_, but _not equally_ distributed. This is the state in which most people are in crowded cities, and who live in the ordinary luxury or the ordinary habits of civilized society, according to the section to which they may belong. It is easy, in such cases, to detect those differences which distinguish this state from what is called condition or perfect health, as we have elsewhere shown[32]. But of course there is _a limit to this power_ in organs of taking on additional or compensating actions; and when this limit is exceeded, then those actions are instituted which we call Disease. The site is _seldom found_ to be that of the original disturbance; and usually for a very plain reason—because there it would be more dangerous, or fatal. It would be scarcely less serious in many cases, even though placed on organs _secondarily_ affected; and therefore it is more usually determined _to the surface_ of the body; where, taking them simply in the order of their greatest number, or frequency, we find the first class of diseased appearances, and which strikingly impress the real nature of _the law_. They are the most numerous, most obviously dependent on general disturbance, and most conservative, as being least fatal. Diseases of the skin are those to which we allude, and which, in the characters I have mentioned, exceed all other diseases.