460 INTRODUCTORY LECTURES. 



cies or varieties of other diseases as distinct genera. Thus the 

 Amphimerina and Tritaeophyia are mere varieties of the tertian 

 and quartan fevers; and in like manner Erythema is to be 

 considered as a species of Phlogosis, and Lumbago and Ischias 

 both as species of the genus Rheumatismus. 



A fifth error relates to what I call the Sequelae, the immedi- 

 ate and constant consequences of a disease. Though these are 

 to be viewed in a different light, they are not to be considered 

 as forming separate genera in the Nosology. Thus the older 

 systems have made genera of Apostema, Abscessus, Gangraena, 

 and Sphacelus, totally separating them from the Phlegmone or 

 Inflammatio : I have marked them, as I think, in their proper 

 place, as sequelae of this disease. It must be obvious, that 

 many diseases in their course change their form to such a de- 

 gree, as to require a practice altogether different from that 

 which was necessary in their former state. Thus, in the fever 

 which I call Synochus, the practice in the end is totally differ- 

 ent from that at the beginning ; but nobody would say that 

 these states ought to form two different genera or even species 

 of diseases. So much for explaining the few cases in which I 

 have introduced this new mode of Nosology ; but I own that in 

 many cases there is some difficulty in admitting this practice. 

 We would do it only when one disease is very constantly a con- 

 sequence of another, and on no occasion arises otherwise. But 

 in many other cases a disease changes to one which is differ- 

 ent, and to which it is only conjoined by certain external circum- 

 stances, and in this last case they ought to be kept as separate 

 genera. I have seen Hydrothorax, for instance, as the conse- 

 quence of Peripneumony ; but it would not have been proper to 

 introduce it as the sequela of Peripneumony. So the fistula 

 in ano is frequently the consequence of haemorrhois, but by no 

 means a constant and necessary one : hence it is to be consider- 

 ed in another place, and under a separate head. The case of 

 most importance where this difficulty occurs, is Phthisis, which 

 I have placed as a sequela of Haemoptoe. I own that I am not 

 clear of being right in doing so ; but it will be of little conse- 

 quence in the system, and will lead to little error. 



The sixth and last error of Nosologists which I shall mention, is 

 that of enumerating diseases of which we have no external symp- 



