16 THE INSPECTION OF FEEDING-STUFFS 



The percentages of protein and fat are required because 

 these two constituents are the most expensive to purchase and 

 are least liable to be produced in sufficient amount in home- 

 grown fodders. 



Protein is made up of a number of substances which contain 

 nitrogen as a distinguishing element. They occur in all the 

 cells of both plant and animal organisms. In plants, protein 

 ,is most abundant in the cells of new shoots, leaves, and the 

 germs of seeds, and in animals it forms the muscles, tendons, 

 and connective tissues, the clotted part of blood, and the curd 

 of milk. Plant protein is the sole source of animal protein in 

 our herbivorous animals, and is indispensable for making 

 growth and milk, and also maintaining an animal in condition 

 for work. 



Fat, as it exists in plants, is almost always oily in consis- 

 tencv. It is most abundant in the seeds, where it is a source 

 of energy to produce activity in the germ as soon as the seed 

 begins to sprout. In the animal, fat is stored in the tissues 

 to furnish a reserve of material for keeping the body warm 

 and producing energy for work. Much of the fat in the food 

 is at once used for these two purposes, and only a surplus is 

 stored. 



Besides protein and fat, cattle foods contain a group of 

 substances called carbohydrates, of which sugar, starch, and 

 gum are well-known types. Such carbohydrates are soluble in 

 ordinarv chemical reagents and usuallv readilv digested bv the 

 animal. They occur in the cells of various parts of plants, 

 and are most abundant in seeds, tubers, and tuberous roots. 

 They furnish the energy for plant activity and the material 

 out of which to build the walls of new cells. Carbohydrates 

 in foods do the same .work in the animal that is done by fat, 

 and can be transformed into fat. They are not as concen- 

 trated as fat, one pound of fat containing as much energy as 

 two and one fourth pounds carbohydrates. In addition to the 

 soluble starch, sugar, and gum, plants contain an insoluble 

 carbohydrate cellulose, which forms the cell walls or frame of 

 the plant. Cellulose, together with insoluble gum, forms the 

 fiber of plants, so expressed in all analyses of plants and 

 foods. 



