26 CLASS I. MAMMALIA. 



of this change is not understood ; but it is presumed to pro- 

 ceed from the office which the blood performs in the nutrition 

 of the bod}' during its circulation, and by which some of its 

 elements are abstracted from it, and combined with the tex- 

 ture of the organs. 



The brain, in man, is the grand centre of sensation and per- 

 ception. It is the instrument through which the mind main- 

 tains its connection with the body; and this connection is ex- 

 tended from the brain to the other parts by means of nerves. 

 The brain is a large organ, of a peculiar texture, occupying 

 the whole of the cavity of the cranium, and consisting of sev- 

 eral distinct parts. Several pairs of nerves proceed from it 

 through different apertures in the skull, and are distributed 

 to the parts about the head, to convey to them the powers of 

 sensation and motion. But besides these, there is another 

 large single nerve passing down into the canal formed by the 

 vertebrae, already described, and supplying the greater part 

 of the body and limbs. 



Through the nerves, impressions are transmitted from all 

 parts of the body to the brain; and on the other hand, all the 

 acts of the will produce an effect upon the different organs 

 by their means. The nerves are necessary to the exercise 

 of the senses (which in man are five : seeing, hearing, smell- 

 ing, tasting, and feeling) ; for, if the nerve going to the organ 

 of either of these senses be injured, the mind no longer re- 

 ceives any impression from them, as happens in the disease 

 of the eye called gutta serena. And if the nerve going to 

 any of the limbs be destroyed or obstructed, both sensation 

 and power of motion in that limb are either destroyed or sus- 

 pended. This happens when a limb, from long-continued 

 pressure upon it, is said to be asleep ; as, in sitting for some 

 time in one particular position, the nerve going to one of the 

 legs is pressed upon, and the connection with the brain being 

 thus interrupted, the consequence is a loss of feeling and mo- 

 tion, which is sometimes so great as to cause the person af- 

 fected to fall down, on attempting to walk. 



The senses, taken altogether, are more perfect in man 

 than in any other animal. Yet in each of them, individually, 

 he is probably excelled by some particular species. Thus, in 

 sight, he is exceeded by the vulture and eagle ; in hearing, 

 by the greater number of rapacious quadrupeds; in smell, by 

 the dog; in taste, by a great many animals ; and in nicety arid 

 delicacy of touch and feeling, by most insects. 



The skeleton and the internal organs of other animals, of 



