FAT.-CARTILAGE. 
59 
pass that keep it in play. It also affords, by its power of re¬ 
sisting the passage of beat, a warm covering to animals that 
are destined to live in cold climates; and it is in these that 
we find it accumulated' to the largest amount. Further, 
being deposited when nourishment is abundant, it serves as a 
store of combustive material, which may be taken back into 
the system, and made use of in time of need. The causes 
which peculiarly contribute to the production of fat, will be 
considered hereafter (§ 162). 
47. Another tissue of which cells form the principal part, 
is that termed Cartilage or gristle. Its simplest state is that 
of a mass of firm substance, composed of 
chondrin (§20), through which are scat¬ 
tered a number of cells, at a greater or less 
distance from one another. In the simple 
cellular cartilages, such as those which 
cover the ends of’the bones where they 
glide over one another so as to form 
moveable joints, no trace of structure can 
be seen in the intervening substance. Fig. is. —Section op 
But in cartilages which have to resist not _ . Caiitila ® e > 
only pressure but also extension or strain, ded in intercellular sub- 
we find the space between the cells partly stance - 
occupied by fibres, which resemble those of ligaments; and 
such are termed fibre-cartilages. . They are found in Man be¬ 
tween the vertebrae of which the spinal column is made up 
(§ 71); and also uniting the bones of the pelvis (§ 645). 
Sometimes, where elasticity is required, the fibres are those 
of the yellow fibrous tissue (§ 23); this is the case with the 
cartilage which forms the external ear. Cartilage is not 
penetrated by blood-vessels, at least in its natural state. The 
blood is brought to its surface by a set of vessels which bulge 
out into dilatations or swellings upon it, so that a large quan¬ 
tity of fluid comes into the immediate neighbourhood of the 
cartilage, being only separated from it by the thin walls of 
the vessels; and it appears that this fluid, or so much of 
it as is required, is absorbed by the nearest cells, and trans¬ 
mitted by them to the cells in the interior, so that the whole 
substance is nourished. This is precisely the mode in which 
the interior of the large sea-weeds (whose tissue consists of 
cells imbedded in a gelatinous substance, and therefore bears 
