50 ON THE EDUCATIONAL VALUE n 



your hearing apparatus, unless you close it up and 

 thereby discover that you become deaf ? 



It would really be much more true to say that 

 Physiology is the experimental science par ex- 

 cellence of all sciences ; that in which there is least 

 to be learnt by mere observation, and that which 

 affords the greatest field for the exercise of those 

 faculties which characterise the experimental 

 philosopher. I confess, if any one were to ask me 

 for a model application of the logic of experiment, 

 I should know no better work to put into his 

 hands than Bernard's late Researches on the 

 Functions of the Liver. 1 



Not to give this lecture a too controversial tone, 

 however, I must only advert to one more doctrine, 

 held by a thinker of our own age and country, 

 whose opinions are worthy of all respect. It is, 

 that the Biological sciences differ from all others, 

 inasmuch as in them classification takes place by 

 type and not by definition. 2 



It is said, in short, that a natural-history class 

 is not capable of being defined that the class 



1 Nouvdle Fonction du Foie considere commc onjane pro- 

 ducteur de matiere sucree chez I'Homme et les Animaux, par 

 M. Claude Bernard. 



2 ' ' Natural Groups given by Type, not by Definition 



The class is steadily fixed, though not precisely limited ; it is 

 given, though not circumscribed ; it is determined, not by a 

 boundary-line without, but by a central point within ; not by 

 what it strictly excludes, but what it eminently includes ; by 

 an example, not by a precept ; in short, instead of Definition 

 we have a Type for our director. A type is an example of any 

 class, for instance, a species of a genus, which is considered as 



