FIRST PRINCIPLES 31 



tactics when hunting are quite different to those of a dog. 

 Its nose gives it general information of the proximity of 

 mice, but it never follows a trail. Its ear tells it with such 

 precision when to spring and in what direction, that the 

 legend has sprung up that a cat can "see in the dark." In 

 truth its eye, which aids in hunting in daylight, is of much 

 less importance to it when darkness approaches than its 

 cheek-bristles, which save it from contact with passive 

 objects, and its ear, which tells it when it is approached by 

 anything that moves. 



While carnivora trust either to the sense of smell, or, like 

 the felidae, to the senses of hearing and smell in following 

 their prey, herbivora trust to the eye for information as to 

 the proximity of their pursuers. Observations of their habits 

 would enable us greatly to extend the list of animals in 

 which one or other of the senses is unusually efficient or 

 unusually deficient. Those named above are but typical 

 examples, and if any one of them which exhibits during life 

 a great reliance upon a particular sense be examined 

 anatomically, it will be found that (i) the organ which 

 serves this sense is obviously well developed ; (2) the nerve 

 which connects the sense-organ with the central nervous 

 system contains an unusually large number of fibres ; (3) 

 that the territory in the brain which is allocated to this sense 

 is more than usually extensive. 



Anatomy and physiology have therefore in a remarkable 

 way confirmed the truth of Leibnitz' dictum, "There can be 

 nothing in the intellect which has not reached it through the 

 senses." Metaphorically speaking, science has given an 

 objective value to the intellect. It has enabled us to speak 

 of the size and form of the brain when we indicate the 

 extent and quality of the mind which uses it. Five instru- 

 ments are played in the orchestra of thought : smell, vision, 

 hearing, taste and feeling, the last named being an organ 

 with several claviers. Vibrations of various kinds strike the 

 keys of these sense-organs. Those which call forth sensa- 



