6 NUTRITION OF FARM ANIMALS 



equivalent to about 7.1 per cent of the dry matter. The pro- 

 portion of ash to dry matter is greater in the young than in the 

 mature animal and greater in the lean than in the fat condition. 

 The more important elements found in the ash are as fol- 

 lows: 



Potassium. This metal is indispensable to plant growth and is 

 found in all parts of the plant, but especially in the active, growing 

 parts. In the animal body it is found abundantly in the tissues, such 

 as the muscles, glands, nerves, etc., while the fluids (blood, plasma, 

 lymph, etc.) contain relatively small amounts of it. 



Sodium. Unlike potassium, sodium is not indispensable to plant 

 growth, although it apparently is useful to the plant under some con- 

 ditions. It is found especially in the stems and leaves of plants, 

 although not so abundantly as potassium. Seeds contain but little 

 of it. In the animal body it is especially abundant in the fluids, 

 which, as just noted, contain relatively little potassium. 



Calcium. Like potassium, calcium is necessary for the growth 

 of plants. It is found especially in the leaves and stems of plants 

 and to a much less extent in the seeds. It appears to be equally 

 essential to the animal and is found in all parts and organs of the body. 

 Its most striking use, however, is in the formation of the skeleton, the 

 mineral portion of which (81) consists chiefly of calcium phosphate 

 and carbonate. Both these compounds being scarcely at all soluble 

 in water, they are well adapted to form the framework of the body. 

 In the skeletons of the higher animals calcium phosphate is the chief 

 mineral ingredient, while in the lower animals like shellfish and 

 Crustacea, the shell, which corresponds to the bones of domestic ani- 

 mals, contains chiefly calcium carbonate. 



Magnesium. Magnesium is also one of the elements essential 

 for plant growth. It is found throughout the plant in smaller amounts 

 than calcium, but is more abundant than the latter in the seeds and 

 seems to aid in seed formation. In the animal body, magnesium 

 usually accompanies calcium, but in much smaller amounts. 



Iron. A small amount of iron is required by the higher plants 

 for the formation of the green coloring matter (chlorophyl) by means 

 of which they assimilate the carbon dioxid of the air. In the ani- 

 mal, iron in small quantity is necessary for the formation of the red 

 coloring matter (haemoglobin) of the blood which is the agent for 

 conveying the oxygen of the air to the tissues. While, therefore, but 

 a very small amount of iron is required by either plants or animals, 1 

 it is nevertheless essential to the most fundamental processes of life. 



1 It is estimated that the blood of an adult man contains about 3 grams of iron. 



