FUNCTIONS OF GANGLION CELLS. 515 



1. Reflection. Many nervous cells are capable of reflecting an 

 impulse received by an afferent nerve ; that is to say they send it 

 by an efferent nerve to some active tissue, such as a muscle or 

 gland. This kind of direction is spoken of as a simple reflex action. 

 For instance, if a grain of red pepper be placed on the tongue, 

 the stimulus soon travels from the peripheral receiving terminal, 

 along an afferent nerve, to its central terminal, which reflects the 

 impulse to the efferent nerve, going to the salivary gland, and the 

 result is an increased secretion of saliva. 



2. Coordination. There are but few reflex acts that do not 

 require the cooperation of several cells, and these work together 

 in an orderly manner, the resulting activity being well arranged 

 and usually adapted to some purpose. The first act of the re- 

 ceiving cells of this reflex centre must then be to distribute and 

 direct the impulse into those channels which lead to groups of cells 

 capable of sending impulses in an orderly and definite direction. 

 This directing and arranging power is spoken of as coordination, 

 and probably is an attribute common to all nerve cells. 



3. Augmentation. Usually the force of the reflected efferent 

 impulse bears a direct relation to the afferent impulse as determined 

 by the strength of the stimulus. Thus if the amount of pepper on 

 the tongue be much increased, not only is the flow of saliva greater, 

 but the stimulus spreads from one central cell to another until the 

 neighboring centres are affected. Thus we often find the lachrymal 

 glands are also influenced by very strong stimulation of the tongue, 

 and pour out their secretion, as is said, "in sympathy" with the 

 mouth glands. But the amount of the afferent impulse is not the 

 only factor in determining the amount of response to be reflected 

 along the efferent channels. Some nerve cells have a distinct 

 power of increasing the amount of response to be given to a given 

 stimulus. When an irritant falls near the laryngeal opening, a 

 very different effect is produced, and the vastly greater response 

 to an equal stimulus depends rather on the augmenting power of 

 some central cells than upon any greater sensibility of the local 

 mechanisms. 



4. Inhibition. Under certain circumstances, such as pre-occu- 

 pation, etc., which will be more fully explained presently, nerve 



