Of all the involuntary organs, the heart, which is the citadel 
of motion, is most protected. To itself belongs a special nervous 
centre, that which feeds it steadily with stimulus for motion ; 
from the cervical ganglia of the 
organic nervous system it receives 
a second or supplementary supply ; 
and from the brain it receives a 
third supply, which, passive under 
ordinary circumstances, can under 
extraordinary circumstances be- 
come active and exert a certain 
controlling power. Then the ar- 
teries which supply the heart with 
blood are the first vessels given off 
from the great feeding arterial 
trunk, and the veins of the heart 
winding independently round it 
empty their contents direct again 
into it. Thus is the heart the most 
perfect of independencies : thus 
during sleep and during wakeful- 
ness it works its own course, and 
taking first care of itself in every 
particular, feeds the rest of the 
body afterwards ; thus even when 
sleep passes into death the heart 
in almost every case continues its 
action for some time after all the 
other parts of the organism are 
in absolute quiescence ; thus in 
hybernating animals the heart con- 
tinues in play during their long 
somnolence ; and thus under the 
insensibility produced by the in- 
halation of narcotic gases and 
vapours, the heart sustains its 
function when every other part 
is temporarily dead. Next the heart in independent action 
is the muscle called the midriff or diaphragm; and as the 
diaphragm is a muscle of inspiration, the respiratory func- 
tion plays second to the circulatory, and the two great functions 
of life are, in sleep, faithfully performed. In sleep of illness 
bordering on sleep of death, how intently we watch for the 
merest trace of breath, and augur that if but a feather be moved 
by it or a mirror dimmed by it, there is yet life. 
In natural sleep then, sleep perfect and deep, that half of our 
nature which is volitional is in the condition of inertia. To 
