578 



THE HUMAN BODY. 



The Pacinian Bodies or Corpuscles (Fig. 171) are found 

 in large numbers in the subcutaneous areolar tissue of the hand 

 and foot, and occasionally in other regions of the skin. But 

 they are also found in internal parts, as on the nerves of 

 tendons and ligaments and on some branches of the solar 

 plexus; and they are very abundant and easily seen in the 

 mesentery of the cat, so that though almost certainly organs 

 in which afferent nerve impulses originate, they are not organs 

 of touch. The corpuscles are oval, often curved on the long 

 and from 1.5 to 2.5 m.m. ( T V- T V inch) in length. 



axis, 



When fresh they have a whitish translucent appearance and 

 are somewhat more opaque in the centre. When magnified 

 each Pacinian body is seen to consist of an almost structure- 

 less core surrounded by many concentric capsules. Each 

 capsule is a layer of imperfectly developed connective tissue 

 having a few very fine fibres, the interstices between which 

 are filled with liquid : each surface of each capsule is formed 

 by a well-marked layer of flat nucleated cells, and the cell 

 layer on the inner side of one capsule is separated from the 

 layer on the outer side of the next by a narrow cleft, which 



is a lymph lacuna. The capsules 

 are usually so closely applied to 

 one another that the lymph spaces 

 between them are almost oblit- 

 erated. A medullated nerve- 

 fibre runs to one pole of each Pa- 

 cinian body and the axis cylinder 

 and medullary sheath are contin- 

 ued through the capsules to the 

 core; the medullary sheath be- 

 coming thinner on the way. The 

 axis cylinder enters the core and 

 runs to near its opposite end, 

 where it ends in a rounded en- 

 largement or sometimes divides 

 into several short branches, each 

 with a knobbed end. 



Touch, or the Pressure 

 Sense. Through the skin we 

 get several kinds of sensation; touch proper, heat and cold, 

 and pain; and we can with more or less accuracy localize 

 chem on the surface of the Body. The interior of the mouth 



6 



FIG. 171. A Pacinian corpuscle, 

 magnified. 



