160 MINERAL INGREDIENTS OF FOOD. 
important. It exists largely in the blood, and in the various 
animal fluids which are secreted from it ; and it is also an 
essential ingredient of most of the solid tissues. Its presence 
obviously tends to prevent that spontaneous decomposition — 
to which organic substances are liable. Phosphorus is chiefly — 
required to be united with fatty matter, to serve as the — 
material of the nervous tissue ; and to be combined with 
oxygen and lime, to form the bone-earth by which the bones 
are consolidated. Sulphur exists in small quantities in several 
animal tissues ; but its part seems by no means so important 
as that performed by phosphorus. Lime is required for the 
consolidation of the bones, and for the production of the 
shells and other hard parts that form the skeletons of the 
Invertebrata. Of the limestone rocks of which a great part 
of the crust of our globe is composed, a very large proportion 
is made up of the remains of animals that formerly existed in 
the ocean. Thus some almost entirely consist of masses of 
Coral, others of beds of Shells, and others of the coverings 
of minute Foraminifera (§ 131). To these mineral ingredients 
we may also add Jron, which is a very important element in 
the red blood of Vertebrated animals. 
167. These substances are contained, more or less abun- 
dantly, in most articles generally used as food ; and where 
they are deficient, the animal suffers in consequence, if they 
be not supplied in any other way. Common Salt exists, in 
no inconsiderable quantity, in the flesh and fluids of animals, 
in milk, and in the egg: it is not so abundant, however, 
in plants ; and the deficiency is usually supplied to herbi- 
yorous animals by some other means. Thus salt is purposely 
mingled with the food of domesticated animals ; and in most 
parts of the world inhabited by wild cattle, there are spots 
where it exists in the soil, and to which they resort to obtain 
- it; such are the “ buffaldlicks” of North America. Phos- 
phorus exists also in the yolk and white of the egg, and in 
milk,—the substances on which the young animal subsists 
during the period of its most rapid growth ; it abounds not 
only in many animal substances used as food, but also (in the 
state of phosphate of lime or bone-earth) in the seeds of many 
plants, especially the grasses; and in smaller quantities it 
is found in the ashes of almost every plant. When flesh, 
bread, fruit, and husks of grain, are used as the chief articles 
