ENLARGEMENT OF PARTS FROM USE. 23 



stronger on the side operated upon, and the ear remained 

 distinctly warmer. 



The relation of irritation upon nerves in connection 

 with overgrowth of dermal structures may be illustrated 

 by the curious defect known as spina bifida occulta. In 

 this malformation the bony arches covering the spinal 

 cord are defective, and the 

 nerves issuing from the cord 

 at this spot are involved in 

 fibrous tissue or compressed 

 by an accumulation of fat. 

 It is no uncommon event 

 to find the skin covering the 

 defective parts of the spine 

 presenting a tuft of hair often 

 many centimetres in length, 

 or the lower limbs may be 

 covered with a crop of thick 

 hair. The common form is 

 shown in fig. 12. 



These facts have been 

 used in a subtle way by Vir- 

 chow. The heads of Polish 



fowls are Surmounted by a FIG. 12. A hairy tuft in the loin, due 



luxuriant tuft of feathers 

 (fig. 13). Underlying this 

 feathery crown in many Polish hens is a defect in the 

 roof of the skull, resembling in many respects the con- 

 dition known in man as meningocele. A study of the 

 effects of spina bifida in man has led Virchow to regard 

 the crown of feathers as the result of irritation, in the 



to a defect in the arches of the spine 

 and irritation of the cord or nerves. 

 (After Fischer.) 



