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11. External causes which are common or habitual, as we 

 have seen, never produce disease without those preparatory 

 changes which establish the state of predisposition; and with the 

 aid of this predisposition they do not at once establish the disease 

 which follows. A person during the exposure to cold may feel 

 only a slight shivering: pneumonia or fever may succeed at a short 

 interval after the exposure. Hence, it is not the property of this 

 cause, viz. cold, to constitute the subsequent disease, nor can it, 

 unless it assimilates, have any immediate share in the state of 

 disease; and whether it assimilates or not, the disease is esta- 

 blished only by progressive causation or by successive changes. 



12. Predisposition then, as belonging to the department which 

 we are considering, is one state (a modified one in comparison to 

 the state of health) of the organic spirit ; the predisposition is pro- 

 duced by changes of the latent properties of the spirit; the con- 

 dition thus produced is so related with an external, as to suffer, 

 upon exposure to it, another change which exhibits symptoms; 

 this change also, or this state, is made by latent properties, in 

 which the external has no share as a cause (accord ing to our defini- 

 tion of a cause) unless it endures with the spirit, and is renewed 

 like the spirit as fast as this latter passes away or dies. 



13. This state, produced conjointly by predisposition and 

 exposure to a related external, is one of disease: it may occur 

 without any assignable external cause, in the way before described. 

 The identity of the diseased state is dependent upon the causes 

 producing it, which cannot be defined because the state itself is 

 not susceptible of analysis. Disease being established, its present 

 form may endure for a time with little variety, or it may run 

 through a series of changes, or it may occupy only one seat, or it 

 may be extended to others, or diffused over the whole system. 



14. During all these changes life still maintains itself by 

 assimilation: that is, life admits all this, which is a considerable 

 variety, and still preserves its character as an assimilating princi- 

 ple. The identity of this principle at any time or in any stage is 

 dependent upon the combinations of its own properties, and its 

 participation of related ones, whether external, derived from a 

 related sphere, or existing in the blood. Let us now return to 

 our example of a disease, that of phthisis pulmonalis, and see how 

 far these doctrines agree with its phenomena, or elucidate the 

 minuter history of its formation. 



15. Predisposition, established by that progressive internal 

 causation before described: this predisposition consisting of a 

 modified or peculiar state of the spirit; this state of the spirit has 

 one seat in the structure of the lungs; this state of the spirit is one 

 which is related with a condition of the atmosphere ; the effect of 

 this relation is perhaps to produce inflammation; the tendency of 

 this inflammation is governed by latent properties, which belong to 

 the spirit: by these it is decided whether the inflammation shall end 

 in resolution, or whether it shall advance towards a quick or slow 

 p P 



