20 PRINCIPLES OF VETEBINABY SCIENCE 



has to do with the movement of liquids, with the maintenance of 

 proper liquid contents of the tissues, with cell movements, and 

 with absorption and secretion." 



• Sulphur is present in small amounts in all animal bodies. It 

 is taken in as a part of the protein molecule, and is largely ex- 

 creted in the urine in the form of sulphates. 



It is customary to divide the constituents of the animal body 

 into (I) inorganic and (II) organic compounds. 



I. Inorganic compounds are water and mineral substances. 

 The former is determined by evaporating the tissues to dryness, 

 the latter by burning them and recovering the ash. 



(1) Water comprises about 56 per cent of the body weight. 

 For the most part it is combined with the other constituents, 

 although a considerable quantity is found as water in the contents 

 of the digestive organs. The muscles of food-producing animals 

 yield almost constantly 78-79 per cent of water. The bodies of 

 lean animals always contain more water in proportion to their 

 weights than do those of fat animals. A young animal has a 

 larger percentage than a mature animal. The importance of 

 water is seen by depriving an animal of all water, when death will 

 occur quicker than if solid food were withheld and water given. 



(2) Mineral substances make up about 5 per cent of the body 

 weight. They largely consist of the salts of sodium, potassium, 

 calcium, magnesium, and iron, in the form of chlorides, sulphates, 

 phosphates, and carbonates. Of these, calcium phosphate, the 

 principle constituent of bones, predominates. Approximately 

 80 per cent of the total ash compounds of fat animals are found 

 in the bones. An animal deprived of all mineral-containing 

 matter will live but a short time. This shows the great impor- 

 tance of these substances. 



II. Organic compounds comprise the balance or about 39 per 

 cent of the weight of the body. They are characterized by 

 always containing carbon. They may be subdivided for study 

 into nitrogenous and non-nitrogenous substances. 



(1) The nitrogenous substances include all the organic com- 

 pounds having nitrogen in their molecules. They have various 

 characteristics and properties. For a complete discussion of 

 these substances references should be made to textbooks on 

 organic chemistry. The most important of this group of highly 

 complex compounds are the proteins. 



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