SECT. XXI. PHYSIOLOGY. 183 
ccccLu1. When the desire of making water 
is urgent, contraction of the levator and sphincter 
ani obstruct the egress of the urine; but they 
seem to operate mostly upon the membranous 
part of the urethra. 
ceccLtiv. The excitement about the orifice of 
the urethra, from the inconsiderate use of can- 
tharides, occasions a difficulty of making water ; 
and inflammation of the bladder itself, causes it 
to be made more frequently, 
