26 MANTJAL OF CATTLE-FEEDING. 



is also fixed witliiu certain limits ; it is plain that the food 

 which the animal receives must also contain the variuns 

 nitrogenous and non-nitrogenous nntiients in proper pro- 

 portions. 



A fodder nsnally contains several or all of the gronps 

 of fiutrlents, bnt may not contain them in the proper pro- 

 portions to satisfy tlxe needs of the organism. Thns, in 

 the examples given above, good hay contains all tlie 

 groups of nutrients in proper proportions, and will sus- 

 tain an herbivorous animal indefinitely ; while oil cake 

 and roots contain an excess, the one of aibnminoids, the 

 other of bodies of the starch or pectin gronps, and so, if 

 capable of sustaining life, do it with a great waste of the 

 one or the other material. They are one-sided foods. 



By combining several one-sided foods, we may prepare 

 a mixture which shall contain all the groups of nntrients 

 in proper propoi'tious and be capable of sustaining an 

 animal economically. Such a niixtnre we may call a ra- 

 tion or a eomj)lete/ood. 



The proportions of the various nntrients in the common 

 fodders and the proper combining of fodders to form ra- 

 tions suitable for various purposes will be treated of in 

 Parts IL and III., and we shall concern ourselves hero 

 only with the occurrence and properties of the nntrients. 

 These it is necessary to consider in order to a proper un- 

 derstanding of the processes of digestion and assimilation. 

 The nntrients are divided into three groups, corresponding 

 to the three gronps of substances in the animal body, viz. : 

 nitrogenous, non-nitrogenous, and mineral substances. 



§ 2. NlTBOGENOUS NXJTJIIENTS. 



Pbotehst. — The predominant nitrogenous constituents 

 of plants resemble closely, in all important particulars. 



