82 THE NERVOUS SYSTEM AND ITS CONSERVATION 



concerned are widely separated, as they run from the 

 receptors to the central apparatus. The olfactory fibers, 

 as we have seen before, plunge into the under surface of 

 the cerebrum itself. The fibers on which taste depends 

 are probably scattered in the trunks of two or three 

 nerves, and their arrangement is thought to be subject to 

 a good deal of individual variation, but it is certain that 

 their place of entrance into the substance of the brain 

 is far back of that for the impulses from the organ of 

 smell. 



Sensations.- We are now in a position to make some 

 general statements based on the outlines of the afferent 

 system which have been given. It is evident that chan- 

 nels to the number of millions exist by which the central 

 nervous system may be approached from without. The 

 impulses moving along these pathways may have been 

 started by changes in mechanical relation-; at the nerve- 

 endings (pressure, tension, vibration). In certain cases 

 they may be the result of temperature changes, either 

 elevations or depressions. In other instances, including 

 the action of the organs of taste, smell, and vision, the 

 immediate source of the impulses must be described as a 

 chemical change. However they may originate, tin- 

 biologic function of all these inflowing currents is to 

 determine adaptive reactions of the reflex type. 



But as human beings we find the sensations which 

 are associated with the arrival of certain of these im- 

 pulses of the greatest interest. Either intensity or novelty 

 ( f -timulation will be likely to insure an echo in conscious- 

 ness. We are usually quite ignorant of the state of most 

 of our internal organs; this does not mean that no im- 

 pulses are ascending from them t-o the brain, but rather 

 that these impulses have a monotonous character. Foster 

 i< re-ponsible for the a-sertion that we should instantly 

 miss the sensory contribution of the viscera if it should 

 cease. To put the proposition somewhat crudely, we may 

 >ay that we have no sen-ations from the alimentary canal, 

 but we should, in all probability, realize a difference if it 



