34 MEMOIR OF BARON HALLER. 
sensibility of the several structures of the animal 
machine, and the degree of sensibility possessed by 
each. The skin is stated to be more sensible than 
any other ; then the muscular fibre, both of which, 
however, derive this property from the nerves ; and 
these being the source of the sensibility of the other 
parts, are themselves, of course, exceedingly sensible. 
Again the marrow, the bones, the internal viscera, 
&c. to which this property had been generally very 
freely conceded, were found to he wholly destitute 
of it. So that all the facts on this point are summed 
up in the following sentence : — “ The sensible parts 
of the body are the nerves themselves, and those 
parts to which they are distributed in the greatest 
abundance. In fact, the nerves alone are sensible 
of themselves, and then whole sensibility resides in 
then- medullary part, which is a production of the 
internal substance of the brain, to which the pia- 
mater furnishes a covering.” 
The author next proceeds to the subject of irri- 
tability, which he demonstrates to he so different 
from sensibility, that the most irritable parts are not 
at all sensible, and the most sensible are not irritable. 
He endeavours in detail to prove both of these pro- 
positions by facts, and then to demonstrate that 
irritability does not depend upon the nerves, but 
upon the inherent constitution of the parts in which 
it resides. After this, the whole variety of struc- 
tures is in the same way examined as it respects 
their irritability, beginning with the nerves, which 
are proved to be not at all irritable ; no more is the 
