Skin Region. Adult Man. Boy aged Twelve. Tip of tongue 1.1 1.1 Palmar surface of tip of finger (index) 2.3 1.7 Red surface of lip 4.5 3.9 Palmar surface of 2nd phalanx of finger 4.5 3.9 Dorsal surface of 3rd phalanx of finger 6.8 4.5 Side of tongue 9.0 6.8 Tongue 27 mm. from tip 9.0 6.8 Plantar surface of distal phalanx of great toe 11.3 6.8 Surface of palm of hand 11.3 9.0 Dorsal surface 2nd phalanx of finger 11.3 9.0 Forehead 22.6 18.0 Back of ankle 22.6 20.3 Back of hand 31.6 22.6 Forearm and leg 40.6 36.1 Dorsal surface of foot 40.6 36.1 Surface on outer border of sternum 45.1 38.8 Back of neck 54.1 36.1 Middle of back 67.1 31.6 to 40.6 Upper arm and thigh 67.1 31.6 to 40.6 TABLE VII.--(_According to Weber’s Law._) Average differences in different regions of skin of sensation of pressure. Forehead } Lips } Dorsum of tongue } 1/30 to 1/40 Cheeks } Temple } Finger nail } Dorsal surface of forearm, leg, } and thigh } Dorsal surface of hand } Dorsal surface of 1st and 2nd } 1/10 to 1/20 phalanges of fingers } Palmar surface of finger } Palmar surface of hand } Flexor surface of forearm } Dorsum of foot } Dorsal surface of toes } Plantar surface of toes } More than 1/10 Sole of foot } Surface of leg and thigh } Thus on the forehead differences of pressure are distinguished when they are increased by 1/30, whereas on the dorsum of the foot they have to be increased by 1/10 to be distinguished. This is carried out by impact of little balls of a light substances such as pith. It may be remarked of these tabulated results that on the one hand they are the results of work extending over some seventy years and numerous observers, and on the other that, broadly looked at, _they all tell the same story_ of stimuli in their incidence on the skin--those of pain, cold, warmth and touch. There is also one thread of origin running through all, and that is that the regions most exposed to the four stimuli show the highest development of specialised function and structure. Some Aspects of the Nervous System.