v.] EDUCATIONAL VALUE OF NATURAL HISTORY SCIENCES. 8 1 



is not a function of a single organ in the body which haa 

 not been determined wholly and solely by experiment. 

 How did Harvey determine the nature of the circulation, 

 except by experiment ? How did Sir Charles Bell de- 

 termine the functions of the roots of the spinal nerves, 

 save by experiment ? How do we know the nsc of a 

 nerve at all, except by experiment ? Nay, how do you 

 know even that your eye is your seeing apparatus, unless 

 you make the experiment of shutting it ; or that your 

 ear is 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 Phy- 

 siology is the experimental science par excellence 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 Eesearches on the Func- 

 tions of the Liver. 1 



Not to give this lecture a too controversial tone, how- 

 ever, 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 



1 "Nouvelle Fonction du Foie considere comme organe producteur do 

 matiere sucree chez 1' 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 circum- 

 scribed ; 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 eminently possessing the characters 

 of the class. All the species which have a greater affinity with this type- 



