454 INTRODUCTORY LECTURES. 



considered as species. It has happened, I think accidentally, that 

 in Nosology, by beginning with the characters of the class, 

 and from thence descending to orders and genera, the term 

 genus has been very universally applied to species ; and, in 

 short, by imitation, I have been led to do the same thing ; for, 

 of the one hundred and thirty- three genera which I established 

 (in my first edition), a hundred are properly species, and admit of 

 no farther division except into varieties: the genera, as there char- 

 acterized, have the ultimate concourse, the steady character of 

 species, and admit of no other subdivision but what are truly 

 varieties. In the other systems the number of genera has 

 amounted to a great many more ; but I maintain that the same 

 proportion holds, that three-fourths, perhaps, of their genera 

 are species in the strict language of method. I have come to 

 my conclusion, that the chief business in Nosology is the for- 

 mation of the character of what I have called genera, and 

 which you truly, for the most part, may consider as species. 



I now proceed to give you some remarks upon the conduct 

 of our Nosology in forming these characters. 



I have said that the characters of diseases are formed by a con- 

 course of various symptoms, every particular of which, in the lan- 

 guage of methodical writers, is a nota or mark : now, in forming 

 the character, the first 9 and the most important rule is, that these 

 marks should be neither more nor fewer than are absolutely ne- 

 cessary. If we have more, we pass from characters or defini- 

 tions to descriptions ; we leave persons in doubt when they find 

 a disease with the strictly essential character, by adding other 

 circumstances which they may suppose to be equally necessary. 

 The Nosologists have been faulty in giving both superfluous 

 and deficient characters. As an instance of superfluous char- 

 acter, take VogePs definition of ' Febris pestilentialis f Febris 

 pandemia, contagiosa, acutissima, in qua bubones aut certe car- 

 bunculi aut vesiculae oriuntur cum leipyria, ingenti siti, spi- 

 ritu, sudore et dejectionibus foetidis, delirio, nausea, vomitu, 

 pulsuque parvo ac obscuro.' The most part of this character is 

 superfluous. The plague may appear without being 6 pande- 

 mia ;' it is often not ' acutissima ;' and the only necessary cir- 

 cumstances are the contagion and eruption. The ' carbunculi, 

 leipyria, ingens sitis,' etc. are in common to the plague with 



