In speaking of affections of the nervous system, Abernethy observes that the brain may be affected by the part injured, and that _then_ it may affect the various organs by a "reflected" operation; but that whatever _may be the mode_ (thus carefully separating the opinion from the fact), "the fact is indisputable." He adds that it may affect some organs more than others, and thus give a character or name to a disease. For example, it might affect the liver, we will say, when the name which would be given would probably be expressive of what was a secondary circumstance—namely, a disturbance of the liver. This does not so frequently happen, perhaps, nor so mischievously in relation to local injuries; but in other cases it is the cause of a great deal of erroneous and misleading nomenclature.
As we have seen, it often occurs that when the organs of the body are disordered, the more salient "symptoms," perhaps the _whole_ of those _observed_, are referred to a secondarily affected organ, and the disease is named from that circumstance. The too frequent result is, that attention is exclusively directed to that organ, whilst the _cause_, being elsewhere, and where there _are no symptoms_, wholly escapes observation.
This is a very important branch of inquiry; and as it closely connects what Abernethy left us with what appears to us to be one of the next things to be clearly made out, we will endeavour to illustrate it.
Suppose a person meet with a severe injury, a cut, bruise, fracture, or any thing that we have seen a hundred times before, and, instead of being succeeded by the _usual_ processes of repair, it be followed by some others: the simple expression of the fact is, that something has interfered with the _usual_ mode and progress of repair; and as former experience has shown us that there was nothing in the nature of the injury to account for this, we are naturally led to look for the explanation of it in the state of the individual. But if the unusual appearance be one which we have agreed to call "Erysipelas," and we are accustomed to see long papers written upon this appearance as a _distinct disease_, we acquire a tendency, as every day's experience shows, to regard it as a kind of abstraction, or as an entity; something composed of precise and definite relations, contained in that particular description of case. Yet these relations may not be in any two successive cases exactly alike. Again, all of them may be subordinate to some more general character, probably a relation without which we cannot readily explain the phenomena; but at which we cannot arrive, because we have not comprehended a sufficient number of facts in our inquiry to include it.