MINERAL METABOLISM OF FARM ANIMALS                          277

at first thought that these were the only minerals essential for the body. It is how.
ever now known that there are other minerals, often present in traces, such as copper,
manganese, iodine, etc., which are also necessary and serve important physiological
functions in the growth and maintenance of the body.

We can classify the known functions of the minerals in the following way :

        (1)  the maintenance of a proper osmotic pressure in the body fluids,
        (2)  the maintenance of the neutrality of the blood and the lymph,
        (3)  the maintenance of the proper physiological balance between various mine-
ral ingredients in the blood,
        (4)  to aid the processes of digestion and absorption, and
        (5)  for the supply of various constituents of growing tissues and of internal
secretions.

It is not necessary to say anything more now with regard to the above classifi-
cation, as the importance of minerals for the abovementioned purposes is well known,

                                      MINERAL REQUIREMENTS.

The question of mineral requirement is not a simple one and the amount varies
in the case of different animals, with age and time. Thus a lactating animal re-
quires a higher percentage of lime than a non-lactating one. Our information with
regard to most elements is scanty ; only definite results are known in the cases of
lime and phosphoric acid. Mineral requirements as a rule are greater for a young
animal than for an aged one, because in addition to the maintenance of the body,
more minerals are necessary for the growing skeleton and tissues.

It has been known for a long time that milk is an ideal diet for the young and
an interesting relation has been discovered between the rate of growth of an animal
and the composition of its mother's milk.3 In Table I the numerical relations are
shown.

                                         TABLE I.

Species

No. of days in which wt. of
the newborn is doubled

Milk of the species contains%

Protein

Ash

CaO

P2O5

Man

180

1.6

0.25

0.049

0.056

Horse

60

2.0

0.38

0.114

0.121

Cow

47

3.5

0.72

0.161

0.189

Goat

22

4.3

0.81

0.191

0.219

Sheep

15

6.5

0.89

0.277

0.269

Pig

14

6.7

1.03

0.395

0.357

Dog

9

7.1

1.01

0.338

0.364

                                                                                                            F 2