THE NERVOUS SYSTEM 309 



in right-handed persons is injured, the power of speech is 

 lost. The comprehension of words and the ability to write, 

 read, and hear language is not lost. With left-handed per- 

 sons, this center is on the right side. 



566. Other Centers in the Cerebrum (Figs. 205, 206).- 

 When the part of the cerebrum that lies behind the ear is 

 destroyed, a loss of the memory 



for the meaning of words may 

 result. One can speak, but his 



words follow each other without .^.^^Auw^^gu A 

 sense or meaning. The sense of " &*=* 



hearing is supposed to be located 

 in the same region. The sense of 

 sight is located in the rear part of 

 the cerebrum. If the rear part 

 of the left hemisphere is de- 

 stroyed, a man is unable to see 

 anything to the right of his nose 



when his eyes are directed straight FlG - 208. The Olfactory Nerve, 

 forward. The sense of smell lies The main nerve ends in the form of a 



bulb on the floor of the skull. The 



at the base of the cerebrum toward fibers branch from this buib like the 



,1 r 4. /T7' ,^/c\ roots from an onion and spread out 



the tront (1< ig. 206). on the walls of the nasal cha mb e r. 



HYGIENE OF THE NERVOUS SYSTEM 



567. Sleep. The cells of the body with all their 

 industry are not tireless, and at intervals require rest 

 (Fig. 210). During sleep the heart beats more slowly, 

 respiration is less rapid, the muscles in general are re- 

 laxed, the gland cells diminish their secretions, and diges- 

 tion is slow. The production of heat is lessened and the 

 body must be protected from cold. Yet consciousness is 

 the only function entirely in abeyance. The sound of a 

 passing vehicle quickens the pulse of the sleeper with- 

 out awaking him; if he is touched, he moves. Sleep 

 is deepest during the second hour, and it then takes a 



