CHAPTER III 



THE GENERAL FUNCTION OF MIND AND BRAIN 



(i) The portion of the body with which mind is associ- 

 ated is the central nervous system. Now the function of 

 the nerve tissue in general is to secure the correlation of 

 different parts of the body in the work of adaptation to its 

 needs and to those of the race. The temperature rises, and 

 a nervous mechanism responds by expanding the smaller 

 arteries, distributing the blood over the surface, and increas- 

 ing the activity of the sweat glands. By these means the 

 blood is kept to an even temperature. A blast of cold air 

 or douche of cold water produces the reverse effects. By 

 running or making any muscular effort we denude the blood 

 of oxygen, and the result is to stimulate the respiratory 

 centre to a greater activity, which causes us by panting to 

 absorb more oxygen. As we run we catch our foot against 

 a stone, and the other foot comes up more quickly to pre- 

 serve the balance, or the hands fly out to protect the face in 

 falling. These adaptations are performed for the most 

 part without the aid of consciousness, which is not quick 

 enough for them, by means of arrangements of sense 

 organs, nerve fibres, nerve centres and muscles, which can 

 in many cases be traced in considerable detail. The nerve 

 fibre is essentially a conductor of excitements. It leads, 

 say, from a cell of the retina to a cell of the mid-brain, and 

 from this cell another fibre will proceed, conducting the 

 excitement to a cell of the occipital lobe. Arrived at the 

 cortex or grey matter of the occipital lobe, the excitement 

 is propagated in a cell of pyramidal ' form, possessing very 

 complex branching processes, which intertwine with the pro- 



