Sensory I)is!iirbaiiccs. 433 



the optic system cause visual weakness (amblyopia) or com- 

 plete blindness (aiiuuirosis) . Auccsthesias of the auditory nerves 

 produce nervous difficulty of hearing- (hy/'iicusis) or com- 

 plete deafness (aiiaciisis). Loss of the sensory jiower of peri])h- 

 eral nerves is sometimes a source of danger for the tissues 

 (for "the senses are the guardians of health"), which become 

 conscious of every injury from the stimulus of pain and arc tlius 

 able to call into action every protective means and measure the 

 body possesses. ' In ansesthesia of the conjunctiva the entrance 

 of foreign bodies to the eye or conjunctival sac is not rcali;-ed, and 

 such substances are not carried off b\- the How of tc;irs. After 

 section of the sensory nerves of the foot, penetration of a nail into 

 the frog- is not evinced by lameness, and the ensuing inflannna- 

 tion and gangrene of the hoof proceed unnoticed — conditions of 

 serious consequence to the life of the subject. Interruption 

 of the sensory portion of the reflex arc puts an end to the tendon 

 reflexes, which cease in anaesthesia of the peripheral nerves because 

 the path of conduction to the reflex centre (pyramids) is broken. 

 If. however, the latter be intact and the communication between 

 the brain and ganglion be destroyed the tendon rcHexes are ex- 

 aggerated (central inhibition may also exist). (Krehl.) 



Loss of the so-called motor senses destroys the coordination of 

 movements and causes the appearance of synijitoms of vertigo (v. p. 

 424). The sense of station of the limbs, which renders i)ossible the 

 acts of walking, standing and especially of orientation in sjiacc. 

 depends upon coordination of the optic and auditory organs, and 

 especially those portions of the latter enclosed in the i)etrous ])or- 

 tion of the temporal bone, as well as of the centripetal sensations 

 from the muscles, tendons, bones, joints, fasciae and skin. 



Where there is loss of a single sense, as that of sight. orientatitMi 

 mav be possible from increased acuteness of other senses (tactile 

 sense, hearing) up to a certain degree Loss of sensory muscle im- 

 pulses or deficient transmission of these impulses or anaesthesia 

 of the cerebral or spinal centres cause more or less loss of power 

 of bodily motion. Disturbances of equilibration of the body occur 

 especially in diseases of the organs in the semicircular canals, in the 

 saccule and utricle, as well as of the central communications of these 

 structures with the cerebellum. How far in these instances we have 

 to deal with a pathological stimulation or pai-al\sis. whether there 

 exist a destructive phenomenon or one caused 1)\- deficient transmis- 

 sion of imi)ulses, are (luestious difficult to decide l)eeause of the 



