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some phenomena or of different phenomena, which so far resemble 

 others, of which we have had a satisfactory experience, as to 

 admit an enumeration under the same class. This evidence is ' 

 founded on analogy to the synthetical test of causation : if we 

 require it to be confirmed, we must employ also the analytical test, 

 as before explained. 



3. Disease may be related either in its own or in another seat. 

 The first, as inflammation of a part, is related with suppuration, or 

 as schirrus is related with cancer; the second, as a disease of a 

 nerve, may produce disorder of the brain, and convulsions over the 

 whole body. 



4. Related disease in the same seat is a progressive causation 

 among the properties which belong to the seat, in the course of 

 which different phenomena are exhibited, according to the rela- 

 tions subsisting between properties. 



5. If a primary produces a secondary disease, the seat of the 

 secondary either receives properties from that of the primary 

 disease, or properties are withheld or abstracted from the seat of 

 the secondary by the state of the primary disease. 



6. We suppose that the properties producing disease are com- 

 municated, when a secondary happens as a consequence of primary 

 disease, the seats of which have no natural relation of the depen- 

 dent kind in the condition of health: the phenomena of irritation 

 and sympathy may be supposed of this kind, as dentition affecting 

 the brain mediately or directly, and producing fits; biliary calcu- 

 lus producing vomiting; inflammation of the liver producing pain 

 of the shoulder, &c. 



7. We conclude that disease is produced by privation of pro- 

 perties in the secondary seat, when the healthy state of this seat 

 is dependent for natural communicated properties upon the seat of 

 the primary disease, and when the function which is dependent 

 upon such communication is lost: thus disease of the brain may 

 paralyze the retina, or produce the same effect in this secondary 

 seat as a ligature upon the optic nerve. 



8. But disease of a primary may produce disease of a secon- 

 dary seat, where a relation subsists of the regular dependent 

 kind by communication of properties, as when the relation is 

 disordered, as perhaps irritation of the brain producing convulsions 

 of the muscles. 



9. It is also possible, according to our causation, that secondary 

 might be produced by primary disease, by privation of properties 

 where no natural dependent relation subsists between the seats; as 

 if a preternatural relation were opened, the effect of which is to 

 render the secondary seat a source of properties to the primary 

 one; thus leaving the state of the secondary seat to be identified 

 by remaining properties, which are deficient in those which would 

 constitute its healthy condition. The discrimination of the mode 

 of causation in these instances must always be diflicult, and the con* 

 elusion very dubious ; such, however, are the alternatives. 



