3. The duration of pain has a very important bearing on the diagnosis of hysteria and neuralgia. Here it may be observed how imposifble it is. from the description of the patient, to form any idea of the exact amount of pain and suffering, or to institute any comparison between the expression of it as employed by different individuals. One will talk composedly during a severe operation ; another looks pale and haggard and seems to be in great pain, perhaps really does suffer much from a mere nervous affection, which exists chiefly in the imagination, and is principally maintained by the attention being continually directed to it. Here, there is the inconsistency that a very unim portant distraction serves to withdraw the attention, and thereby removes all recollection of its existence and every indication of its continuance. A third person suffers severely from paroxysms of pain, which no amount of pre-occu pation can prevent, no distraction during its continuance can suspend ; yet in this case there may be no structural change to account for the presence of pain. The power of distracting the attention is often the only distinction between that which is unimportant and transitory and that which is of grave import and exceedingly untractable until its duration and recurrence, and the exhaustion it produces, point out its reality.
Duration is, therefore, a poifit of great value in judging of the intensity and importance of expressions of pain. a. Severe pain of long continuance must have told on the health of the sufferer. b. The pain of a nervous affec tion may be actually greater than that accompanying a severe disease in the same locality; but the continuance of disease produces far .more important changes than can result from the mere persistence of pain. c. When local pain is of short duration, if it be only one of the features of long-standing illness by which the constitution has not been affected, it must be regarded as of minor importance.
4. A certain amount of caution is necessary in adopting the patient's description of the order of sequence of symptoms. It is remarkable how, in slowly advancinir maladies, nature accommodates herself so completely to immense alterations in structure, that until some unusual event occurs, the patient is utterly unconscious of any deviation from health ; or it may be there is only a sense of malaise, without the possibility of tracing this feeling to its cause, or of naming any single symptom which has attended it. Sud denly some change occurs of which the patient becomes cognizant, and then other sensations which previously existed take form and shape in his mind, and consequently find place in his description, after that which is in reality their effect and not their cause.
Again, so intimate are the relations maintained between all parts of the body, that it may not be in the very locality in which disease has commenced that symptoms of its presence first arise ; and hence sometimes the first feeling of illness does not directly point to its true seat. This must be corrected b7 knowledge of the theory of disease, and the various symptoms by which it is accompanied.
With these qualifications, the first real deviation from health is of much value in leading U8 back to the true seat of disease.
5. Most diseases have a certain established course, which, either in broad and general outline, or even in minor detail, is followed by au the examples coming under observation ; and although we cannot prescribe the exact limits of these sequences, either in days or weeks. yet there are periods of greater or less duration during which certain phenomena must present themselves, or else our diagnosis has been utterly at fault. This fact forms one of the elements of prognosis, and points out its association with a just discrimination of the nature of a malady in the first instance.