66 THE FEEDING OF ANIMALS 



they are constructed, although the proportions are 

 unlike. 



NITROGEN COMPOUNDS THAT ARE NON-PROTEINS 



In the usual method for determining the proteins of a 

 food by multiplying the total nitrogen present by a fac- 

 tor, there is included in the calculation nitrogen that does 

 not come from true proteins, but from compounds that 

 possess physical and chemical properties greatly removed 

 from those which characterize albumin and other true 

 proteins. Their office as nutrients is probably less com- 

 prehensive than that of the proteins. 



85. Amino-acids and amides. These compounds re- 

 sult from the union of organic acids and the group NH 2 . 

 Whether the resulting compound is an amino-acid or an 

 amide depends upon the manner of combination. Cer- 

 tain of the amino-acids may be produced in the labora- 

 tory by synthesis, but in the main they are obtained 

 from the cleavage of protein through the action of acids 

 or alkalies or ferments (enzyms). They are found abun- 

 dantly in the alimentary canal during the digestion of food 

 as a result of the action of the digestive enzyms on pro- 

 teins. Amides occur in plants. Asparagine is an amide of 

 amino-succinic acid, first found in young asparagus shoots, 

 and glutamine is an amide of amino-glutaric acid, found in 

 germinating pumpkin seeds. They are soluble in water, and 

 consequently are diffusible throughout the plant tissues. 

 It is believed that such amides are forms in which the 

 nitrogen compounds of the plant are transferred from one 

 part to another, as, for instance, from the stem to the seed. 

 It has generally been held that these bodies are more abun- 

 dant in young plants than in mature. A larger part of the 

 nitrogen of roots and tubers is found in these compounds 



