2 THE CHE'MTSTRY OF CATTLE FEEDING 



Carbon Potassium 



Oxygen Magnesium 



Nitrogen Calcium 



Hydrogen Iron 



Sulphur Chlorine 



Phosphorus Fluorine 



Sodium Silicon 



These substances are not present in the same relative 

 proportions in the two types. Animals, for instance, usually 

 contain larger proportions of nitrogen and phosphorus than 

 plants. Some of the elements mentioned above do not form 

 part of the tissues. They are found only, or chiefly, in the 

 juices or fluids where they perform various functions of greater 

 or less importance in the economy of the organism. 



Of those which actually enter into the composition of the 

 tissues it may be said, in general, that they are combined in 

 a similar manner. In other words, plants and animals are 

 composed, riot only of the same chemical elements, but also, 

 to a large extent, of the same kinds of chemical compounds. 



This fact is of fundamental importance. It could not be 

 deduced from any d priori considerations ; and it is the more 

 striking in view of the numerous and complex chemical 

 changes which the food of animals undergoes in the processes 

 of digestion and after absorption into the blood. 



The more important chemical compounds found in plants 

 and animals may be classified as (a) nitrogenous substances, 

 (b) fats or oils, (c) carbohydrates, (rf) mineral salts, and (e) water. 

 It must be clearly understood that, with the exception of water, 

 these are not the names of particular substances but of groups 

 or classes of compounds. Each of the groups includes many 

 different compounds which must be further classified by 

 sub-division according to their properties. 



Certain compounds occur only in plants, others only in 

 animals ; and some are peculiar to particular kinds or varieties 

 of plant or animal. The fats or oils found in plants are not 

 identical with those of animal origin. Palm oil, for instance, 

 is not the same as lard. The fat of one kind of plant or one 

 kind of animal is not exactly the same as that of any other 



