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CHAP. II. Origin of Disease in one Seat. 



1. DISEASE (or symptoms) may commence in any given 

 seat from a progressive causation which is uninterrupted, or from 

 preparatory changes which have rested in the state of predisposition ; 

 and then a new causation is begun, which terminates in the exhibi- 

 tion of symptoms, or in death. By these principles the question 

 must be answered, why does disease commence] 



2. When the changes which terminate in disease are uninter- 

 rupted, each internal change is a predisposition, which is related 

 with existing causes. When one series terminates in a predisposition, 

 the progression towards disease is renewed, or the state immediately 

 established, only by the operation of causes which, though perhaps 

 common and natural ones, did not obtain when the former changes 

 rested in the state of predisposition. This latter has been exempli- 

 fied in physiology, if is necessary to illustrate both a little further by 

 a short comparison with the histories of disease. 



3. In our example of consumption, we have supposed no ex- 

 ternal assignable cause; but admitting that such a cause did obtain, 

 its first operation is not to establish the symptoms which identify the 

 disease; that is, the lungs do not at once, by a casual exposure to 

 cold, become ulcerated, &c.; but a trivial symptom, as a slight 

 cough, or some change preparatory to the complete establishment 

 of the disease, is the result of the operation of this cause. From 

 this change the series is uninterruptedly progressive; for the relation 

 is constant between each change and the existing causes. This is 

 an instance of the production of symptoms in an uninterrupted 

 series. The history of predisposition might be different; it might 

 consist of interrupted gradations, which are next to be exemplified. 



4. A woman might have a small tumour in the breast ; it might 

 remain, without change for many years: this tumour has formed by 

 a train of causation indicated in the preceding pages; this series has 

 rested in a state of predisposition to the condition which the 

 tumour afterwards assumes; it rests in this state, because its con- 

 stituents no longer hold a relation of change with existing causes. 

 If this state is altered, it must be from the influence of some new 

 cause; this cause may be produced from change going on internally 

 among connected agents, which having attained a certain state, may 

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