THE TEMPERATURE-SENSE. 



differences of from T V to Y V (from 200 : 220 to 200 : 210 gm.). The anterior 

 surface of the leg and thigh resembled the forearm. Then followed the 

 back of the foot and of the toes ; the sensitiveness was much less on the 

 plantar aspect of the toes, the sole of the foot, and on the posterior aspect 

 of the thigh and leg. Dohrn tried to determine the smallest increase of 

 weight that in the presence of a weight of i gm. could be appreciated by 

 different portions of the skin. This was for the third phalanx of the 

 finger 0.499 gm., the back of the foot 0.5 gm., the second phalanx of 

 the finger 0.771 gm., the first phalanx 0.82 gm., the leg i gm., the back 

 of the hand 1.156 gm.,the palm of the hand 1.018 gm, the patella 1.5 

 gm., the forearm 1.99 gm., the sternum 3 gm., the umbilical region 3.5 

 gm., the back 3.8 gm. The delicate lanugo-hairs of the skin are espe- 

 cially sensitive to pressure. 



5 Too long a time must not elapse between the application of two 

 weights, but as much as 100 seconds may elapse if the difference in 

 weight is in the ratio of 4 : 5. 



6. The after-effect in connection with the pressure-sense is especially 

 pronounced when pressure of considerable amount is applied for some 

 time. Even slight pressures, however, when applied repeatedly and 

 successively, must be separated by intervals of at least from g-^-g- to T |-g- 

 second in order to be perceived individually. More rapid succession 

 causes confusion of the impressions. Valentin found that, when he held 

 the finger-tip against a wheel set with blunt teeth, he had the impression 

 of a smooth edge if the teeth struck the skin at the intervals mentioned ; 

 when the revolution was slower, each tooth excited a separate pressure- 

 sensation. Vibrations of strings are recognized . as such when they 

 make from 1506 to 1552 vibrations in the' second. 



7. It is remarkable that pressure effected by thoroughly uniform 

 compression of a part of the body, for example by immersing an arm 

 in mercury, is not perceived as such; the ringer dipped in mercury 

 perceives the pressure only at the limit of the fluid on the palmar 

 surface of the finger. 



8. The points that are sensitive to pressure are also sensitive to 

 traction. If pressure and traction are applied alternately to the same 

 area of the skin, the distinction is possible only when the irritation has 

 a certain extent, duration and intensity. Traction (acting somewhat 

 as a negative pressure) is tested by the application of small pieces of 

 plaster, which can be drawn upon by means of a thread. The forehead 

 and the temple are capable of recognizing 0.05 gm. of traction-force, 

 the finger-tips and the lower lip 0.5 gm., the forearm 9 gm., the leg 20 

 gm. 



THE TEMPERATURE-SENSE. 



Through the temperature-sense information is obtained as to the 

 variations of the temperature of the surface of the body. The 

 temperature-sense is subserved by specific nerve-endings having a 

 punctate arrangement. These temperature-points are arranged in chains 

 or lines, which usually are slightly curved. They radiate from certain 

 points of the skin (chiefly from the roots of the hairs). The chains of 

 the cold-points do not coincide, as a rule, with those of the heat-points, 

 although both have the same areas of radiation. These lines of points 

 are frequently not complete, but are indicated only by isolated points, 



