*34 



THE PRESSURE SENSE. 



on the back, 4 to 6 mm. ; breast, 0*8 ; abdomen, 1*5 to 2 ; cheek, 0*4 to 0'6 ; 

 upper arm, 0*6 to 0*8 ; fore-arm, 0*5 ; back of the hand, 0*3 to 0*6 ; palm, 0*1 to 

 0*5 ; leg, 0-8 to 2 ; back of foot, 0*8 to 1 ; sole of foot, 0*8 to 1 mm. 



Methods. 1. Place, on the part of the skin to be investigated, different weights, one after 

 the other, and ascertain what perceptions they give rise to, and the sense of the difference of 

 pressure* to which they give rise. We must be careful to exclude differences of temperature and 

 prevent the displacement of the weights the weights must always be placed on the same spot, 

 and the skin should be covered beforehand with a disc, while the muscular sense must be 

 eliminated ( 430). [This is done by supporting the hand or part of the skin which is being 

 tested, so that the action of all the muscles is excluded.] 2. A process is attached to a balance 

 and made to touch the skin, while by placing weights in the scale-pan or removing them, we 



Fig. 619. 

 Landois' mercurial balance for testing the pressure sense. 



In^ordef WvmTfV" Wdgh -! th \ 1 ^ nan . ex P erim ented on is able to distinguish (Dohrn). 3. 

 tWom T\ ^ e nec f 8Slt y , of changing the weights, A. Eulenburg invented his bra. 

 SS Tj^X^FT* ? n **"! P ri ^r aS as P iral Pring paper-clip or balance, 

 shows at on tL I ***** Q ^ skln an(f is de pressed by tlie spring An index 



can be verv easHvCiT *S *? T' d *? in . strume nt is so arranged that the presssure 

 waves ^%^nthSS^' ^T* I . ?? elastic tab *. in which he can produce 

 TsTulse-w^ mustbe before ^ey are experienced 



(L 619) The Wm ,u 18 W Upon the 8kin 5 ' Landois uses a mercurial balance 

 Kil Jm /Jf*? I a balance V) " 10ves u P n two knife-edges (O, 0), and is carried on the 

 *f^^^f^7>^^ (T \. ne arm f the beam * Prided with a screw (m) 

 calibrated tub? m ^ilZ^-^ 11 be m VecL The other arm <*) P ass ^ into a vert ica 

 weih?75) and which Si 'f 18 he P^sure-pad (P), which can be loaded as desired by a 

 adkun n* b\ireTt 7 CM ho? ? ^ T? the P art of the skin to be tested (H). From an 

 the arrow , to oni Lrf nf ll C L a T P (A) ' T? CUry Can *** throu g h a tube iu the direction of 

 me arrows, to one part of the balance and into the tube (R). On the stop-cock (h) being 





