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. 
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 
luxuriant tuft of feathers 
(fig. 13). Underlying this 
Fic. r2.—A hairy tuft in the loin, due 
to a defect in the arches of the spine 
and irritation of the cord or nerves. 
(After Fischer.) 
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 
In | 
