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4. When a secondary succeeds to a primary disease, if they are 

 to be considered according to the rules laid down, as hqlding a 

 causative relation with each other; in every instance of related 

 disease one of the following results ensues: 1st, either the primary 

 disease ceases upon the occurrence of the secondary; or, 2nd, the 

 primary disease preserves or changes its character, according to the 

 relations of the properties of the secondary, with those of the 

 primary seat; or, 3rd, one of the preceding results on the primary 

 disease happens either by a relation with more than one secondary 

 seat, or by an extension from a secondary seat by which, perhaps 

 through many mediate relations, the primary seat may come to be 

 affected, according to one of the above results, by processes to which 

 it gave origin ; or, 4th, the primary disease may produce a secon- 

 dary, and the affection may from thence be further extended, and 

 the disease in each seat might run the same course as if only one 

 seat were the subject of it. This elaborate division admits of being 

 reduced to two classes of related disease, viz. 1. those secondary 

 diseases which tend to cure the primary; and, 2. those which do not 

 tend to such a result, but on the contrary add only to the com- 

 plexity of the symptoms, and perhaps ultimately convert disease 

 into death. 



5. That certain diseases are related with each other in the way 

 of cause and effect, is a remark which is cotemporary with the earliest 

 records of medical observation. It is also a piece of information, 

 popular with all classes, that the cure of one disease, whether spon- 

 taneous or by art, is sometimes followed by the occurrence of 

 another. Thus, it is common to expect a favourable change of 

 some internal disease, upon the occurrence of a cutaneous eruption; 

 thus, also, it has fallen under the observation of the ignorant and 

 unprofessional, that a cutaneous disease cured by external applica- 

 tions often produces visceral disease. The language of the vulgar 

 in the first of these cases is, that the internal disease is coming out ; 

 in the second, that the disease of the skin is thrown in y or settled 

 upon the lungs, for instance. To all physicians the class of facts 

 here adverted to is well known ; they have been made the subject of 

 express treatises, and have been remarked upon in every age, and 

 explained according to the prevailing pathology of the limes. But 

 the professors of medicine have of late been rather sceptical with 

 respect to the assigned agency of the phenomena in question, though 

 it is not improbable that their exception was taken rather against the 

 doctrine of humours, &c. by which the phenomena were explained, 

 than against the more modest inferences which they might be al- 

 lowed to furnish. To all physicians of the present day the class of 

 facts, designated as those of related disease, is well known : by some, 

 these facts are not suffered to furnish an inference of a relation, 

 that is, they are considered independent of each other; others 

 admit the relation, and explain it in the language of the vulgar; 

 others say that one disease, instead of falling or being thrown upon 

 another part, is converted into a disease of another part : some 

 Q 9 



