346 



ELEMENTS OF PHYSIOLOGY 



625. Cooperation of Eye and Touch. The infant reaches 

 for the moon. It is learning by reaching for things seen to 

 judge of distance. By feeling of 

 things seen it soon learns to tell 

 round things from flat things by 

 sight alone. The aid that touch gives 

 to the sense of sight is illustrated by 

 the case of a boy who had been blind 

 from birth and received sight at the 

 age of twelve years by means of a sur- 

 gical operation. At first he could not 

 distinguish a globe from a circular 

 card until he had touched them. 

 He had become acquainted with dogs 

 and cats by feeling but did not know 



FIG. 223. Diagram 

 Course of the Retinal Nerve 

 Fibers. 



of the them apart by sight alone. One day 



Light from A strikes the outer part 



he picked up the cat and .recognized 

 for the first time the connection be- 

 tween the new sense of sight and the 

 these parts go to the right half o i^ familiar one of touch. On put- 



of the brain, B. A/ represents 



the nose. The spots A and A ting the cat down he said, " So, puss, 

 I shall know you next time." 



HEARING 



on the retinae are habitually 

 stimulated together. 



626. The ear may be described in three parts, the outer, 

 middle, and inner ear (Fig. 224). The outer ear consists 

 of the cartilaginous concha, the part that is usually spoken 

 of as the " ear," and the meatus, the canal leading into the 

 head from the lower part of the concha. Which part of 

 the concha is not cartilaginous but fatty tissue ? Part of 

 the wall of the meatus is of cartilage, but the deeper part 

 has a wall of bone. The entrance to the meatus is guarded 

 by hairs, and its wall is covered with a bitter wax secreted 

 by glands in the lining. Its inner end is closed by the 

 tympanic membrane, which is sometimes called the driim, 



