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 

 lo 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 Iron, 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- 

 vorous 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 " buffalo-licks" 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 



