LAWS OF LIFE, HEALTH, ETC. 247 
From birth to death there is a very gradual increase of the 
earthy constituents, which renders strength and firmness up to 
a certain point, when afurther preponderance causes brittleness, 
as inold age. A simple experiment will prove the above. If 
a bone (a long one is best) is burned in the fire, the gelatinous 
or animal matter will be separated and destroyed, leaving the 
earthy matter withoutadhesion. Again, ifthe bone is steeped in 
dilute muriatic acid sufficiently long, all the earthy matter will 
bedissolved, and you may winditroundyour hand. The bones, 
like every other part of the body, except the nails, hair, and 
chrystalline lens of the eye, are supplied with blood-vessels 
and nerves, and are covered with a delicate membrane called 
the periosteum, from which parts of the bones lost through 
decay may be renewed. 
THE MUSCLES, 
which are about 500 in number, are the organs of motion, 
being formed of contractile tissue, and in direct communication 
with the brain. In the healthy state they are its obedient 
servants, This does not, however, apply to the involuntary 
muscles, which perform the digestive and assimilative functions, 
and the heart, which may be considered as one muscle, keeping 
up its contracting and relaxing, orsystoleand diastolemovements 
from early foetal life to death. The muscles are said to have 
their origin in the fixed parts to which they are drawn in 
contraction and their insertion into the bone, or portion of the 
bone, designed to be moved. Their contracting power is caused 
by a stimulus from the nerve, which, when it is withdrawn, they 
relax. ‘Their rapidity of movement seems to be marvellous, 
as in rapid speaking, playing musical instruments, such as the 
piano, where a large number of muscles are employed con- 
tractingand relaxing. The beautiful adaptation of the muscles 
to the bones gives the body itsformand symmetry. In this short 
sketch we cannot go further into detail. We only wish to 
impress on the minds of our readers the fact that as they form 
the greatest part of our body, we should be careful to use and 
exercise them aright. This latter is essential to their truly 
healthy development, as instance the arm of the blacksmith. 
