GRASSES OF IOWA. 469 



"become part of the blood as the result of the breaking down 

 of the food materials and tissues in the body, or in other words, 

 the residue or ashes of muscular action. A large or an excess- 

 ive amount of protein in the food material has a tendency to 

 require an extra effort on the part of the kidneys to throw off 

 from the body the resulting residues. 



The study of the food material naturally divides itself under 

 two considerations: 



I. The amount of protein and of carbohydrates necessary 

 for the animal, and the correct proportion of these two classes 

 which will result in keeping the animal in the most healthy 

 condition. 



II. The use of an excess of one class of food material over 

 the correct amount necessary results not only in an injury to 

 the animal, but is largely a loss to the person feeding under 

 such conditions. 



The inorganic part of the food material supplies certain 

 demands made by the growth and maintenance of the animal; 

 for example, calcium phosphate supplies the material forming 

 the bone substance. Salt furnishes the supply of hydro- 

 chloric acid in the gastric juice and aids in the digestion of 

 food by the pepsin, and iron aids in blood formation. 



The object of digestion is a process designed by nature to 

 prepare the food material so that it can be readily absorbed by 

 the animal. We may, as a means of illustration, compare the 

 changes that take place during digestion t) the process of 

 some manufacturing plant where the food is crushed and 

 ground by the teeth, the starch changed to sugar, the albu- 

 minoids which are insoluble rendered to soluble, or in other 

 words, changed to peptones, and then as a final proces? the 

 material is subjected to the combined action of a number of 

 agencies which prevent any waste in the material intended for 

 nourishing the animal. 



The amount of food necessary for certain animals and the 

 relative proportions of protein and the carbohydrates and fats 

 has been the subject of a great number of investigations, and 

 is a valuable field for study. Dr. Emil Wolff originated a table 

 of feeding standards which has been widely used. The table 

 is as follows: 



