926 SENSE OF SPACE. 



The same influence is exerted by the : application of- cold to the skin, by 

 the action of the anode, strong stretching of the skin, for example of the 

 abdominal walls during pregnancy, likewise previous exertion of the 

 muscles situated beneath the cutaneous area ; as well as certain poisons : 

 atropin, daturin, morphin, strychnin, alcohol, potassium bromid, 

 cannabin, and chloral hydrate. 



The shortest distances in millimeters at which two compass points were 

 recognized as separate by an adult are as follows (the analogous figures for a 

 boy twelve years old are enclosed in parenthesis) : Tip of the tongue i . i mm. (i. i) ; 

 palmar aspect of the third phalanx of the finger 2-2.3 C 1 -?); re d part of the lip 

 4.5 (3.9); palmar aspect of the second phalanx of the finger 4-4. 5 (3.9); palmar 

 aspect of the first phalanx of the finger 5-5.5; dorsal aspect of the third phalanx 

 of the finger 6.8 (4.5); tip of the nose 6.8 (4.5); palmar aspect of the head of a 

 metacarpal bone 5-5.5-6.8 (4.5); thenar eminence 6.5-7 ; hypothenar eminence 

 5.5-6; middle of the palm of the hand 8-9; middle and border of the back of the 

 tongue, white part of the lips, metacarpus of the thumb 9 (6.8) ; plantar aspect of 

 the third phalanx of the great toe 11.3 (6.8) ; dorsal aspect of the second phalanx 

 of a finger 11.3 (9); cheek 11.3 (9); eyelid 11.3 (9); middle of the hard palate 

 13.5 (11.3); palmar aspect of the lower third of the forearm 15; skin over the 

 front part of the zygoma 15.8 (11.3); plantar aspect of the metatarsal bone of 

 the toe 15.8 (9) ; dorsal aspect of the first phalanx of a finger 15.8 (9) ; dorsal aspect 

 of a metacarpal bone 18 (13.5) ; inner aspect of lip 20.3 (13.5) ; skin over the pos- 

 terior part of the zygoma 22.6 (15.8) ; lower portion of the forehead 22.6 (18) ; pos- 

 terior portion of the heel, 22.6 (20.3) ; lower portion of the occiput 27.1 (22.6) ; back 

 of the hand 31.6 (22.6); submental region 33.8 (22.6) ; top of the head 33.8 (22.6); 

 patella 36.1 (31.6); sacrum and gluteal region 40.6 (33.8); forearm and leg 40.6 

 (36.1) ; back of the foot near the toes 40.6 (36.1) ; sternum 45.1 (33.8) ; upper por- 

 tion of the neck 54.1 (36.1); spine (fifth dorsal vertebra) , lower dorsal and lumbar 

 54.1; middle portion of the neck 67.7: arm, thigh, and middle of the back 67.7 

 (31.6-40.6). 



By experimenting according to method 4 (p. 925), it is found that the spatial 

 sense is best developed in the face and in the furrows of the finger-joints; then 

 follow: the palm of the hand, the back of the hand (error as high as i cm.), the 

 neck, the arm (error up to 2 cm.) , the clavicular region, the upper arm, the abdomen 

 (error up to 3 cm.), the chest, the back of the foot, the leg (error up to 4 cm.), 

 thigh (error up to 7 cm.). The touching of one toe is often confused. Pregnant 

 women localize poorly upon the abdomen. 



Illusions of the spatial sense are quite common. The most striking are: (i) 

 A uniform movement over the surface of the skin seems to be more rapid 

 on those parts that possess the most delicate spatial sense. (2) If the skin 

 be merely touched by two compass-points, they seem further apart than when 

 they are stroked over the skin. (3) A sphere provided with short rods appears 

 larger than one with long rods. ( 4 ) When two fingers are crossed, small objects 

 placed between them seem to be doubled (Aristotle's experiment). (5) If, how- 

 ever, the terminal phalanges of two fingers are first touched in the normal position 

 ot the fingers, and then "the same places when the fingers are crossed, the two points 

 touched seem to lie in the same relative position. (6) If flaps of skin are trans- 

 planted, for example a flap with a pedicle from the forehead to the nose, the patient 

 will often for months have the feeling in the new portion of the nose as though it 

 were the forehead, providing the nerves of the forehead remain intact. 



Many attempts have been made to explain the phenomena of the spatial 



.se. &. H. Weber started from the assumption that one and the same nerve- 



iber, passing from the brain to the skin could receive and transmit only one kind 



)f impression within the area supplied by it. He gave the name of sensory circle 



each region of the skin to which a single fiber was distributed. If two 



.mpressions act simultaneously upon the tactile apparatus, they are recognized 



Louble if one or more sensory circles lie between the two points. This inter- 



3n, based on anatomical considerations, cannot be reconciled with the fact 



the circles of sensation may be reduced in size by practice, and, further, 



that only one sensation arises when the two points are so applied that, although 



ther apart than the diameter of such a circle, they at times lie upon two ad- 



es, and at other times upon two other circles separated by a third. 



