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went to the seat of the secondary, these properties, being those oi 

 inflammation, should produce inflammation of the bowels rather 

 than a diarrhoea, which rarely occms in inflammation of the bowels. 

 If the identical disease of a primary is in metastasis transferred to a 

 secondary seat, as the character of the secondary is commonly very 

 different from that of the primary disease, it is necessary to infer 

 that the identical nature of the primary disease is liable to be modi- 

 tied by peculiarities which belong to the secondary seat. Laying 

 aside the word metastasis, by some it is said that one disease is con- 

 verted into another. This term " conversion" is one which either 

 does not carry a clear meaning, or if a certain meaning shall be 

 agreed upon, it implies a theory which will require proof's. Either 

 trie word " conversion" implies the operation of a cause which pro- 

 duces its own similitude, as one man is converted to the same 

 opinion as another; or as life converts constituents of food and air 

 into life, &c. ; or else it is employed with greater latitude, as water 

 is converted into ice, &c, or as wine is converted into vinegar; if 

 employed in the former sense, it is not applicable in the present sub- 

 ject, for we cannot suppose that the properties constituting inflam- 

 mation are made those of a diarrhcea, or that they are converted 

 into an effusion of blood, &c.: if the term is employed in the latter 

 sense it designates no one species of causation, but may apply to any, 

 as cold converts water into ice, that is, cold and water make ice; 

 or sulphuric acid will convert magnesia into a neutral salt, that is, 

 sulphuric acid and magnesia constitute a neutral salt. I would not 

 be understood that the term is violently objectionable, or that some- 

 thing may not be said on both sides respecting its use in these cases, 

 but its implication in the first definition will bear a cavil, and iu the 

 second it is no term of distinction. 



11. The first class of related disease, viz. that in which a 

 primary ceases upon the occurrence of a secondary disease, may be 

 called substitution of disease, which merely expresses the fact that 

 one disease has taken place, while another has ceased; the word 

 " vicarious," which is familiar in medicine, expresses the same thing. 

 The second class of related disease, viz. that in which the primary 

 does not cease upon the occurrence of the secondary, may Le called 

 related extension of disease (the causative relation being in both 

 cases assumed upon the grounds before stated). 



12. The examples of substituted disease are very numerous, 

 and it is upon this experience of their frequency that the relation of 

 cause and effect in some or other of its modes comes to be inferred 

 to subsist very generally between them. We cannot, however, upon 

 this point compel belief. 



13. Although the examples of substituted disease are very 

 numerous, they are not sitliiciently regular to admit a classification of 

 those primary diseases which are likely to be cured (to beg an ex- 

 pression) by the occurrence of secondary ones. We can rarely, 

 (owing to this irregularity) perhaps we can in no case anticipate the 

 i ure of a primary disease by a secondary one; that is, we cannot 



