438 
POPULAE SCIENCE EEVIEW. 
that much, of the tone or tension of parts depends upon a 
tonic condition of the muscles ; but all the soft struc- 
tures of the body, including muscle, are put, or liable to be 
put, in a state of tone by other means. All parts of the 
body are packed closely together, and bound up by the skin 
and other more or less unyielding membranes, having many 
points of adhesion to each other and to the bony framework. 
Consequently, when a soft part increases in bulk or diminishes, 
it causes, in the respective cases, a strained or a relaxed con- 
dition of these membranes, and increased or diminished pressure 
upon adjacent parts. Variation in the bulk of an organ is to 
be referred partly to an alteration in the quantity of fluids 
retained in it, and partly to an alteration in the quantity of its 
solid substance. Variation in bulk due to the flrst cause is 
well seen when cold or exceeding mental depression causes 
the blood to leave the superficial parts^ in the altered volume 
and tension of the facial members and of the fingers. The 
disappearance of much of the blood from these organs is quite 
evident in these cases, and the features become pinched 
and collapsed, and the fingers shrunken, so as even to allow 
rings to fall off them which ordinarily fit on them closely. 
Such great but temporary variations in the distension of parts 
by fluids have, however, little to do with our present subject, 
and are only adduced as illustrations. But it is found that a 
state of healthy functional activity in an organ always gives it 
an increased fulness from the larger quantity of fluids which 
then permeate it, thus giving it the degree of tone character- 
istic of health. Variation in bulk, and therefore tension, 
through change in the quantity of tissue-substance in an 
organ, is yery important, because on this quantity greatly 
depends the extent of its contractile power, and of the cohe- 
sion of its parts. The structures of the body, more particularly 
in its soft parts, are constantly changing in the matter of 
which they are composed, the present matter altering in 
nature, is being thrown off as waste, in place of which new 
matter is being taken up from the blood. These processes of 
waste and repair are usually balanced in their effects. 
But, a fact familiar to every one, parts of the body and the 
body itself are liable, even of a person not considered ill, to 
variations in their fulness and weight from many causes, such 
as differences in the mode of living, in the amount and nature 
of exercise taken in the degree of quietness or anxiety of 
mind, &c. But in many diseases this variation becomes more 
strikingly noticeable. The disease may be such as to unfit the 
organism to take due nourishment, or, to prevent further 
mischief from the disease, it may be necessary to lessen the 
quantity and nutritive value of the diet ordinarily taken ; in 
