Page:Brain Volume 31 Part 3.pdf/26

 {| class="nerve-division-table" ! Number by which the hair is known ! Pressure in grammes ! Measured radii in μ ! Total area in mm.² ! Radius of a circle of the same area in μ ! Pressure per unit area ! Tension
 * + Tactile Hairs
 * 1
 * 0·04
 * 30 × 54
 * 0·005
 * 40
 * 8 grm./mm.²
 * 1 grm./mm.
 * 2
 * 0·1
 * 45·5 × 57·5
 * 0·0085
 * 52
 * 12 grm./mm.²
 * 2 grm./mm.
 * 3
 * 0·21
 * 55 × 90
 * 0·015
 * 70
 * 14 grm./mm.²
 * 3 grm./mm.
 * 4
 * 0·23
 * 40 × 80
 * 0·011
 * 58
 * 21 grm./mm.²
 * 4 grm./mm.
 * 5
 * 0·36
 * 60 × 90
 * 0·017
 * 73·5
 * 21 grm./mm.²
 * 5 grm./mm.
 * 8
 * 0·88
 * 100 × 120
 * 0·0377
 * 110
 * 23 grm./mm.²
 * 8 grm./mm.
 * }
 * 100 × 120
 * 0·0377
 * 110
 * 23 grm./mm.²
 * 8 grm./mm.
 * }

Towards the end of our research, we received a second set of hairs from Professor von Frey which were useful in measuring the punctate pressure capable of producing cutaneous pain. These so-called "pain-hairs" exercise considerably greater pressure than those used for testing cutaneous tactile sensibility, and are graduated by calculating the pressure per unit area. Thus, we shall speak of the tactile hairs as No. 5, No. 8, &c, whilst the so-called "pain-hairs" will be known by the pressure they exert per unit area.

Throughout the greater part of this research, we have attempted to measure roughly the force applied in pricking the skin by means of an instrument we have called the "algesimeter." It consists essentially of a sharp needle attached by a flexible joint to a rigid rod. This is weighted and slides freely through two supports placed 10 cm. apart projecting horizontally from a vertical brass bar. When the needle is brought into contact with the skin, the full pressure of the weight on the rod would be