ANIMAL NUTRITION 175 



they are found in water. They supply the animal with heat 

 and energy. Starches and sugars are carbohydrates. Car- 

 bohydrates are also contained in potatoes, in wheat flour, 

 oatmeal and other cereals. 



3. Fats. These are composed almost entirely of carbon, 

 hydrogen and oxygen with a high percentage of carbon. 

 Like the carbohydrates they supply heat and bodily energy, 

 having per pound more than twice the value of the carbo- 

 hydrates. Fats are found in butter, meat fats and the oils 

 of various nuts. The fats stored up in the body are mainly 

 derived from the carbohydrate food. 



4. Mineral Compounds. These hjave varied composition, 

 but very few contain carbon. They serve a variety of pur- 

 poses in the body. Water and the salts of sodium and cal- 

 cium are the most important articles of this class of foods. 



118. Development of a Science of Animal Nutrition. 

 The science of animal nutrition had its beginning in 1859, 

 when Grouven suggested the first feeding standard for farm 

 animals. Grouven's standard was based upon the total 

 amount of crude protein, carbohydrates, and fat contained 

 in the material fed. Later work has shown that this was 

 an irrational basis, because of the variation in the digesti- 

 bility of these proximate constituents in different animal 

 feeds. It is even more necessary to consider the digesti- 

 bility of the feed for animals than it is to consider the avail- 

 ability of a fertilizing material for plants, because, after a 

 certain length of time, the feed undigested is voided by the 

 animal, while the unavailable plant food remains in the soil 

 and may later be made available by natural agencies. 



In 1864, Dr. Emil von Wolff presented a table of feed- 

 ing standards based on the amount of digestible nutrients 

 contained in each particular feeding stuff. Wolff's standard 

 has siace furnished the basis for rational feeding methods. 

 In 1874, ten years after Wolff published his standard, 

 Dr. Atwater brought it to the attention of the American 

 people, and in 1880 Armsby published his " Manual of 



