344 THE NERVE SYSTEM 



depend upon the peculiarities inherent in the central 

 and peripheral end-organs, regardless of its con- 

 struction and the character of the stimuli (Brubaker's 

 Physiology) . 



Special Stimuli. These comprise the group which 

 act upon the nerves of special sense and give rise to 

 conscious sensations, through the highly specialized 

 end-organs, which transfer the nerve impulse to the 

 filaments of the nerves in relation with them. 



The afferent nerves (sensor) convey the impulse to 

 the higher conscious centres, in response to the special 

 stimuli, as follows: (1) Light or etheral vibra- 

 tions act upon the end-organs of the optic nerve 

 in the retina (sight and light); (2) sounds act upon 

 the end-organs of the auditory nerve (hearing) in the 

 ear; heat or vibrations of the air act upon the end- 

 organs in the skin; (4) chemic agents act upon the 

 end-organs of the olfactory (smell) and gustatory 

 (taste) nerves of the nose and tongue respectively. 



The efferent nerves (motor) convey impulses to the 

 muscles, glands, etc., in response to stimuli which 

 are supposed to arise as a result of a molecular dis- 

 turbance in the central nerve cell, a combination of 

 physical and chemic processes attended by the libera- 

 tion of energy, which passes from molecule to molecule. 

 The passage of the nerve impulse is accompanied by 

 changes of electric tension. 



Thus, to sum up, all nerve impulses have their 

 origin in the nerve cells or neurones, and these millions 

 of associated neurones are the basis of all nerve activity. 

 A theory has been created to simplify the understand- 

 ing of nerve cell activity. It is called the neurone theory 

 of Waldeyer, who explains it, based on the works of 

 Golgi, Cajal, Forel, and others, as follows: (1) Each 

 neurone is a distinct and separate entity; (2) the 

 collaterals and other terminals of the neurones form 

 no connections among themselves; (3) neurones are 



