450 INTRODUCTORY LECTURES. 



and attended to their common relations, if we had not brought 

 them into genera, orders, and classes ; and without that, we 

 would miss a great many particulars which relate to our subject. 

 Now, I say the same is true with regard to diseases : the char- 

 acters of a class, order, and genus, must enter more or less into 

 the character of every species ; they all relate to facts which are 

 of consequence in our Pathology. 



I shall have occasion to acknowledge that I have myself not 

 kept free of every doubtful matter in my present execution of 

 this subject ; although I still maintain that I have with great 

 propriety prosecuted the attempt upon this plan. I have, for 

 instance, made one general division of diseases into Systematic 

 and Local ; my first three classes (Pyrexiae, Neuroses, Cach- 

 exiae,) comprehend the former, and the fourth (Locales) the 

 latter ; but I own that the constitutional or local nature of a 

 disease is not easily determined by what the nosological char- 

 acter should be determined by, viz. the external marks ; and, 

 therefore, doubts will arise with regard to it on many occasions. 

 Thus the lex systematis made me place among local diseases 

 the Amenorrhoea, though I own that it is but seldom local, 

 and much more frequently a systematic disease. And so with 

 respect to other diseases several doubts may arise ; but these 

 will always lead to questions in Pathology. 



Another difficulty which has been suggested with respect to 

 Nosology, and which is indeed the greatest, is the difficulty of 

 distinguishing between what we call Species and what we call 

 Varieties of diseases. I shall not at present undertake to shew 

 that this difficulty may be easily obviated ; but, in the mean 

 time, I say, that it affords no proper objection to a methodical 

 arrangement. The very same difficulty occurred in Botany ; 

 and it goes so far, that even in the system of the very elegant 

 and accurate Tournefort, one third at least, and probably more, 

 of the plants which he enumerates under the title of species, are 

 truly now allowed to be merely varieties. The botanists were 

 early aware of this, and saw the impropriety of prosecuting the 

 distinction of varieties, which are infinitely variable and no ways 

 steady, and for the knowledge of which there is very little use, as 

 in extremely few instances can we say that the qualities or virtues 

 of plants are different in consequence of the variety. The bo- 



